Muffled Sound On Phone Calls

I have noted muffled sounds on my telephone calls. This includes via the ear speaker, on speakerphone, and using bluetooth headphones. If I try to play a song, the audio is perfect which means the speaker on the bottom is fine.

Here are the interventions I have attempted thus far with no resolution:

1. installed the most recent iOS 14.2
2. rebooted the phone
3. turned airplane mode on and off
4. turned bluetooth on an off
5. reset network settings
6. assured that the cellular signal was fine
7. enabled wi-fi calling
8. I have cleaned the phone thoroughly
9. case has been removed
10. calls muffled with earbuds but music is flawless
11. it also occurs while using FaceTime.

Can someone please help?

Thanks.