Same problem here with brand new Iphone 13 pro. Voice cuts out on speakerphone also. That is the main way I use the phone. At the moment I have to answer with it in my ear speaker and talk into the phone that way. Thsat is better for the other caller I called. But... That is NOT acceptable for a $1599. new phone as of 10 days ago!! I have appointment at the Genius bar in Knoxville today at 12:15pm. I will update this with what they say. Otherwise I will be forced to return it and go back to my Iphone 10 until I find a new one. (Hard to get right now, limited inventory.
So frustrating!