I have faced this problem for months. My wife has a iphone 11 pro. I have an iphone 10. When we communicate on Facetime her voice and video are choppy. I hear every second or third word. I thought the phone was defective. I then tested it with friends who have various iphones (not iphone 11). No issues at all with Facetime. I then tested it with another iphone 11 pro. Same choppy conversation.
The problem appears to be with some sort of feedback through the non iphone 11 phone. I discovered this by testing it with my bluetooth headset. The problem stopped immediately. I then tested this by muting my phone (iphone 10). The problem again disappeared. As soon as i turned off the mute the problem started again.
Her iphone was reset to factory settings, the TMobile SIM card was changed, calls to Apple Support, etc. did not resolve anything.
Try muting the non iphone 11 phone. (The one receiving the choppy audio).
i put in another call to Apple Support and will contact them again when I have her phone available for testing.
PLEASE POST YOUR RESULTS.