Had this problem with my 7+; upgraded to an iPhone XS Max running 12.4 (now) and still have the same problem:
Phone volume on Bluetooth is super low. When I play music through the same bluetooth device,I have no issues. When I go to Settings | Volume Limit and play with the volume, sometimes it fixes it in real time, but the problem always comes back.
iPhone XS
When you are on the phone with Bluetooth, and actually in a call, use the side buttons to turn the volume up. You should see "Bluetooth" in the volume popup on the screen, and that should raise the volume for you. It seems that just the volume for the Bluetooth device is not enough.
When you are on the phone with Bluetooth, and actually in a call, use the side buttons to turn the volume up. You should see "Bluetooth" in the volume popup on the screen, and that should raise the volume for you. It seems that just the volume for the Bluetooth device is not enough.
Bluetooth phone call volume too low
