Lowest call volume too loud

I see a lot of posts about this issue, and there seems to be a lot of confusion about the actual symptom. This is something that happens with all phone calls, not only with certain callers. Here's what I see:

• When using the phone to listen to music, watch videos, etc., the volume buttons can reduce the sound all the way to zero.
• When I use a phone calling app (either the built-in Phone app or other collaboration apps such as Microsoft Teams, which mimic phone call functionality), the function of the volume buttons changes. Now, the phone prevents the volume from being turned down all the way. This appears to be a deliberate design decision in iOS: someone decided that if you're on a phone call, it doesn't make sense to turn the volume all the way down. You can see the difference when you attempt to lower the volume all the way to zero: When listening to audio, the "Volume Down" button can reduce the volume to zero, and the white volume bar becomes totally gray. When in a phone call, the white volume bar will not go all the way to the bottom no matter how many times you press the "Volume Down" button. I have observed this behavior both with AirPods and when using the phone itself with no headphones.
• This design decision makes some sense -- I can see why a user wouldn't want call volume to be reduced completely so no sound comes out at all. But the minimum level of sound should be reduced so it's at a comfortable level, knowing that the user can't reduce it any further.
• This problem is especially annoying when using AirPods, because you can't just remove the AirPods from your ears and hold them at a distance.

Hey there, and welcome to Apple Support Communities, Ctrlz0!

From our understanding, when talking to someone on the phone, the volume of the caller is louder than expected. We can certainly understand your concern and can help provide some insight.

To start, go through the suggestions found here to help limit the volume on calls: Adjust the volume on iPhone - Apple Support

Kindest regards!

Hey Ctrlz0.

Thanks for following up.

Changing the volume on the iPhone is the only way to lower the sound on a call. If this only happens with certain callers, it may be something on their end that needs to be adjusted. 

We hope you have a great day.