After 5 to 10 minutes into a phone call the person I am talking to can no longer hear me but I can still hear them. I call back and it works fine for a few minutes. In every other respect the phone seems to work fine. This problem occurs for all calls and makes no difference whether I call them on my iPhone or they call me. I do not use Bluetooth. It has IOS 12.4.5, I think it's up to date.