Now if you look in the dnsmasq log at var/log/pihole/pihole.log you will see the queries from all clients. You can look for the IP of the iPhone and see if the queries from that device are reaching Pi-hole, and if so, how they are being processed by Pi-hole.
What would cause a site to reply with SERVFAIL when using the Pihole for DNS but when using Cloudflare or Google or any other upstream provider for DNS, it resolves just fine?
SERVFAIL indicates that the upstream DNS resolver was unable to complete the transaction.
What is the output of the following command from the Pi terminal?
sudo grep -v '#\|^$' -R /etc/unbound/unbound.conf*
/etc/unbound/unbound.conf:include: "/etc/unbound/unbound.conf.d/*.conf"
/etc/unbound/unbound.conf.d/root-auto-trust-anchor-file.conf:server:
/etc/unbound/unbound.conf.d/root-auto-trust-anchor-file.conf: auto-trust-anchor-file: "/var/lib/unbound/root.key"
/etc/unbound/unbound.conf.d/qname-minimisation.conf:server:
/etc/unbound/unbound.conf.d/qname-minimisation.conf: qname-minimisation: yes
/etc/unbound/unbound.conf.d/use-own-identity.conf:server:
/etc/unbound/unbound.conf.d/use-own-identity.conf: hide-identity: no
/etc/unbound/unbound.conf.d/use-own-identity.conf: identity: ""
/etc/unbound/unbound.conf.d/use-own-identity.conf: hide-version: no
/etc/unbound/unbound.conf.d/use-own-identity.conf: version: ""
/etc/unbound/unbound.conf.d/use-own-identity.conf: hide-trustanchor: no
/etc/unbound/unbound.conf.d/use-expired-records.conf:server:
/etc/unbound/unbound.conf.d/use-expired-records.conf:
/etc/unbound/unbound.conf.d/use-expired-records.conf:
/etc/unbound/unbound.conf.d/use-expired-records.conf: serve-expired: yes
/etc/unbound/unbound.conf.d/use-expired-records.conf: serve-expired-ttl: 0
/etc/unbound/unbound.conf.d/use-expired-records.conf: serve-expired-ttl-reset: yes
/etc/unbound/unbound.conf.d/use-multithreaded-udp.conf:server:
/etc/unbound/unbound.conf.d/use-multithreaded-udp.conf: so-reuseport: yes
/etc/unbound/unbound.conf.d/pi-hole.conf:server:
/etc/unbound/unbound.conf.d/pi-hole.conf: verbosity: 1
/etc/unbound/unbound.conf.d/pi-hole.conf: interface: 127.0.0.1
/etc/unbound/unbound.conf.d/pi-hole.conf: port: 5335
/etc/unbound/unbound.conf.d/pi-hole.conf: do-ip4: yes
/etc/unbound/unbound.conf.d/pi-hole.conf: do-udp: yes
/etc/unbound/unbound.conf.d/pi-hole.conf: do-tcp: yes
/etc/unbound/unbound.conf.d/pi-hole.conf: do-ip6: no
/etc/unbound/unbound.conf.d/pi-hole.conf: prefer-ip6: no
/etc/unbound/unbound.conf.d/pi-hole.conf: root-hints: "/var/lib/unbound/root.hints"
/etc/unbound/unbound.conf.d/pi-hole.conf: harden-glue: yes
/etc/unbound/unbound.conf.d/pi-hole.conf: harden-dnssec-stripped: yes
/etc/unbound/unbound.conf.d/pi-hole.conf: use-caps-for-id: no
/etc/unbound/unbound.conf.d/pi-hole.conf: edns-buffer-size: 1232
/etc/unbound/unbound.conf.d/pi-hole.conf: prefetch: yes
/etc/unbound/unbound.conf.d/pi-hole.conf: num-threads: 1
/etc/unbound/unbound.conf.d/pi-hole.conf: so-rcvbuf: 1m
/etc/unbound/unbound.conf.d/pi-hole.conf: private-address: 192.168.0.0/16
/etc/unbound/unbound.conf.d/pi-hole.conf: private-address: 169.254.0.0/16
/etc/unbound/unbound.conf.d/pi-hole.conf: private-address: 172.16.0.0/12
/etc/unbound/unbound.conf.d/pi-hole.conf: private-address: 10.0.0.0/8
/etc/unbound/unbound.conf.d/pi-hole.conf: private-address: fd00::/8
/etc/unbound/unbound.conf.d/pi-hole.conf: private-address: fe80::/10
/etc/unbound/unbound.conf.d/remote-control.conf:remote-control:
/etc/unbound/unbound.conf.d/remote-control.conf: control-enable: yes
/etc/unbound/unbound.conf.d/use-large-buffers.conf:server:
/etc/unbound/unbound.conf.d/use-large-buffers.conf: so-rcvbuf: 8m
/etc/unbound/unbound.conf.d/use-large-buffers.conf: so-sndbuf: 8m
/etc/unbound/unbound.conf.d/use-safe-edns-buffer.conf:server:
/etc/unbound/unbound.conf.d/use-safe-edns-buffer.conf: edns-buffer-size: 1472
/etc/unbound/unbound.conf.d/use-optimized-threads.conf:server:
/etc/unbound/unbound.conf.d/use-optimized-threads.conf: num-threads: 4
/etc/unbound/unbound.conf.d/use-prefetch.conf:server:
/etc/unbound/unbound.conf.d/use-prefetch.conf: prefetch: yes
/etc/unbound/unbound.conf.d/use-prefetch.conf: prefetch-key: yes
/etc/unbound/unbound.conf.d/use-optimized-caches.conf:server:
/etc/unbound/unbound.conf.d/use-optimized-caches.conf: msg-cache-slabs: 4
/etc/unbound/unbound.conf.d/use-optimized-caches.conf: rrset-cache-slabs: 4
/etc/unbound/unbound.conf.d/use-optimized-caches.conf: infra-cache-slabs: 4
/etc/unbound/unbound.conf.d/use-optimized-caches.conf: key-cache-slabs: 4
/etc/unbound/unbound.conf.d/use-optimized-caches.conf: rrset-cache-size: 128m
/etc/unbound/unbound.conf.d/use-optimized-caches.conf: msg-cache-size: 64m
/etc/unbound/unbound.conf.d/use-optimized-caches.conf: key-cache-size: 64m
/etc/unbound/unbound.conf.d/use-optimized-caches.conf: neg-cache-size: 64m
/etc/unbound/unbound.conf.d/use-unbound-control.conf:remote-control:
/etc/unbound/unbound.conf.d/use-unbound-control.conf: control-enable: yes
/etc/unbound/unbound.conf.d/use-unbound-control.conf: server-key-file: /etc/unbound/unbound_server.key
/etc/unbound/unbound.conf.d/use-unbound-control.conf: server-cert-file: /etc/unbound/unbound_server.pem
/etc/unbound/unbound.conf.d/use-unbound-control.conf: control-key-file: /etc/unbound/unbound_control.key
/etc/unbound/unbound.conf.d/use-unbound-control.conf: control-cert-file: /etc/unbound/unbound_control.pem
/etc/unbound/unbound.conf.d/use-extended-statistics.conf:server:
/etc/unbound/unbound.conf.d/use-extended-statistics.conf: verbosity: 1
/etc/unbound/unbound.conf.d/use-extended-statistics.conf: statistics-interval: 600
/etc/unbound/unbound.conf.d/use-extended-statistics.conf: extended-statistics: yes
/etc/unbound/unbound.conf.d/use-extended-statistics.conf: statistics-cumulative: yes
You can up verbosity like described below:
Ow and I still see duplicates:
I don't know where these are coming from 
I didn't make these files, such as use-extended-statistics.conf or add anything into them.
I dont know either.
You can check whats in the Unbound package with below:
dpkg -L unbound
And search wih below if that use-extended-statistics.conf file comes with some other package:
dpkg -S use-extended-statistics.conf
This is the contents of use-extended-statistics.conf:
# DEFINE SERVER
server:
# EXTENDED STATISTICS
# Note: Set desired verbosity
# use-entended-statistics.conf is called after unbound.conf
# so we can override the verbosity set there
# Verbosity levels are
# 1 - operational information
# 2 - detailed operational information
# 3 - query level information
# 4 - algorithm level information
# 5 - client level information
verbosity: 1
# Note: Number of seconds between statistics log updates
# Rarely required often, but needing to be fresh when it
# is, I have chosen ten minutes as my 'sweet spot'
statistics-interval: 600
# Note: Enable extended statistics
extended-statistics: yes
# Note: Enable cumulative statistics
statistics-cumulative: yes
Didn't see those files anywhere in the unbound package and dpkg-query: no path found matching pattern *use-extended-statistics.conf* was returned for looking in all packages.
Should I just reinstall Pihole and Unbound from scratch?
All below files usualy dont come with a basic default unbound setup when following the official guide:
use-own-identity.conf
use-expired-records.conf
use-multithreaded-udp.conf
remote-control.conf
use-large-buffers.conf
use-optimized-threads.conf
use-prefetch.conf
use-optimized-caches.conf
use-unbound-control.conf
use-extended-statistics.conf
As long as those config files keep interfering, I wont be able to help.
Yeah, I honestly have no idea where those came from.
No results found for unbound "use-own-identity.conf" "use-expired-records.conf".
Okay, okay, okay...those results are bringing back memories from when I originally installed Pihole and Unbound 3-4 years ago. I think I followed a guide that guy made and it resulted in those config files based on "their setup".
I think I should just probably uninstall Pihole and Unbound and start over.
Just reinstall unbound only!
Purge everything with below:
sudo apt purge unbound
Make sure no config file is left behind with below:
sudo rm -r /etc/unbound
And follow the guide to the letter:
Do you have a link for that guide?
I think it was a guide referencing this post by the same person you found: saint-lascivious comments on DoH on PiHole?
Okay, will do this now and report back if the same issues are being seen.