The problem (where my voice breaks up for the other person) happens for me frequently when on the telephone with speaker phone, holding my iPhone 13 Pro in front of my face. Recently I tried restarting and re-calling, setting the phone down or holding it in different positions, switching speaker phone off and holding the phone up to the side of my head, and connecting to my AirPod Pro bluetooth headphones. The person on the other end said I kept cutting out no matter what I tried. I tested all three microphones (by recording front video, back video, and voice memo), and they work fine, so that isn't the problem. I suspect it is a dysfunctional noise cancellation system overreacting to normal background noises like heater vents or the fridge. If only I was able to turn off that noise cancellation, I could find out!