By the way, it's not only AirPods.
I am experiencing issues with a few other devices where the iPhone start disconnecting/reconnecting on repeat:
First is bluetooth motorbike intercom. The iPhone will start disconnecting and reconnecting even when idle (no music or conversations happening). On voice calls behaviour is very similar to what happens with Airpods.
I also have a small bluetooth device that can be used for gps navigation that relies on the iPhone to give GPS positioning and driving directions, and again, it would disconnect and reconnect continously.
Airdrops to the iPhone from a Mac won't work most of the time or be extremely slow.
See my thread here too:
https://forums.macrumors.com/threads/iphone-13-data-transfer-issues-of-bluetooth-and-wifi.2441252/
The only way to – temporarily – stop this behaviour is to restart the iPhone.
This is becoming the be a bigger problem than just not being able to have voice calls.
I'd consider buying a new iPhone, but I don't want to spend 1 grand and end up having the exact same issues.