Sound on phone calls is low
During phone calls the voice volume is too low
iPhone 11, iOS 13
A large number of users are reporting this problem on different iPhone models. I believe I have tried all of the suggestions that have been made in the responses to these low volume reports. I have to use the speaker to hear most phone conversations. I have reported this issue on the Apple feedback page. It would be helpful if you reported the problem there as well. That's the best way to report this issue. Apple does not monitor this forum.
iPhone 8 / iOS v13.6