iPhone 11 calls breaking up for caller

My iPhone 11 (purchased from AT&T in IL in Jan 2020) is suddenly now experiencing distorted calls. The speaker audio is crystal clear for me, but the person on the other end of the call says they can only hear every other word, or I sound computerized. This occurs whether I am using the handset, speakerphone or Apple wired earbuds.

I have tried every suggestion on the Apple support site to test the audio (such as making a video, voice memo) and the audio is clear to me, so this is only happening during phone calls. I have tried force resetting my phone, toggling in and out of Airplane Mode, taking off the case, turning off my Bluetooth… nothing works.

From a quick search of Google, it looks like this is a common problem with the 11 and that it occurs with both AT&T and Verizon service.

What can I do to resolve this?