Wow! I can't believe there are five pages on this issue without even the slightest hint at the right solution.
I spoke to a Senior Advisor at Apple when the same issue surfaced for me. The answer he gave me seems
to have done the trick.
There is more than one mic on the iPhone 13. In fact, there are three. The one at the bottom, next to the speakers, is the
microphone that you use when you are holding the phone up to your mouth (which makes sense because
it is closest to your mouth when holding the phone). The second one is in the notch at the top of the phone on the front.
According to this Senior Advisor, when in Speaker phone mode, the microphone that is in use is the one on the BACK
and at the TOP of the phone (next to the camera lenses). If you set the phone down on its back you are smothering or muffling that microphone. The same problem occurs if you are holding the phone in a way where your hand or finger covers over that area. It seems logical since if you are teleconferencing, then the microphone should be on the same side as the video lenses, not on the opposite side, right?
Look, this Senior Advisor could be a pathological liar but I no longer get any complaints of a muffled or hard-to hear voice. He was also the ONLY Senior Advisor who was able to correctly diagnose and assist me with a complicated problem that required reinstalling the Monterey OS. And yet AT&T is the first Google link on this query and gets it totally wrong! Evidently, the Apple specs do not even mention the mic in the camera system!
Will someone at Apple please verify this? Which of the microphones is the one that is activated in speaker phone mode?
I believe I have the answer but would appreciate some validation. You don't want us looking foolish speaking into the wrong microphone, do you?