This sounds like your Pi-hole is being by-passed, either via IPv6 or via an iOS feature labeled Connectivity Assist, available and possibly active by default on iOS 27 and above (I don't run any iPhones, so can't verify).
There are reports that Connectivity Assist -when active- seems to route DNS lookups to public DNS servers via its mobile data connection, even when connected to a wifi network.
For checking potential IPv6 by-passes, please upload a debug log and post just the token URL that is generated after the log is uploaded by running the following command from the Pi-hole host terminal:
sudo pihole -d
or if you run your Pi-hole as a Docker container:
docker exec -it <pihole-container-name-or-id> pihole -d
where you substitute <pihole-container-name-or-id> as required.