The issue I am facing: resolve dns.mydomain.com on static ip using android so my mobile devices can resolve on mobile network on my pihole remotely.
Details about my system:
Believe for android I need a domain SRV record to point dns.mydomain.com, what I'm unsure of is if the pihole needs to be set to resolve dns.mydomain.com or will resolve all requests on port 53
What I have changed since installing Pi-hole:
DNS port 53 reachable to pihole from Internet checking port open externally. 
SRV record update 24-48hours
Thank you
***Update ***
looking at dns.adguard.com they have an A name record as they do resolving dns.mydomain.com on mxtoolbox.
dns.adguard.com are not using srv records.
I have duplication of above and still with dns.mydomain.com and port 53 open and forwarding to pihole-no joy on pfsense router.
Should this be dns over tls