Quality of iphone 13mini speaker during dialing and phone calls

My partner and I both upgraded four phones from iphone 7 and iphone se to iphone 13 mini last month. We are both using ios ,15.1.1. We are disappointed with the speaker performance during phone calls. The sound is muffled, discordant and unclear. This occurs only when using the speaker for dialing and the voice of the callers during the phone call. The speakers function well when listening to music and videos. This is very disappointing, and not expected from an upgrade.

Has anyone encountered this problem? And what is the solution?