access-control: would still need to be 0.0.0.0/0 allow unless you can identify the range of possible WAN IPs when your Android phone is on cellular networking.
https://github.com/RMerl/asuswrt-merlin.ng/wiki/User-scripts#ddns-start
This explains the /jffs/scripts/ddns-start script you would need to create. But it would take some fancy sed commands to replace the WAN IP in unbound.conf with $1 in the ddns-start script. Quite possible, but takes some work to do reliably. Martineau is very good at swapping values in the unbound.conf script.
Does the DoT connection work yet from the WAN? Once it does, you could enable logging to see the source IPs from the Internet to determine if they fall within a more specific IP range.
Skynet will block bad IPs regardless of port, so no special configuration required.
I could not test yet. I will test and put the feedback here tomorrow morning.
Do I have to put these firewall changes in some file to make it persistent?