How to Fix Quiet Bluetooth Phone Calls on iPhone
Lately my iPhone has been driving me crazy. Whenever I talk on the phone while on Bluetooth the volume of the person I'm talking to is really low, even though it's turned all the way up.
I couldn't point to when it actually started I just knew it was really annoying. If I get a call, which happens a couple times a day (I know, weird to talk on the phone), I am usually doing something else that requires both of my hands so I often use my Bluetooth earbuds to do it. After a conversation with my dad last night I finally started Googling the problem. It was not immediately evident.
Someone posted on the Apple discussions forum about this exact thing, saying that it had happened since switching to iOS 11. The first answer was obvious and stupid, but not necessarily uncalled for when they said "Try adjusting the volume on your device while on Bluetooth." I of course had only tried to turn up the call volume while using Bluetooth because it wasn't a problem any other time. I clicked to look through all of the answers and found a partial solution, the missing info I accidentally found myself.
Another respondent said to go into Settings > Music and change the Volume Limit to make sure it is maxed out. I did that and it was. I called myself on my office phone and still quiet as a mouse. Then I turned it almost all the way down to see what that sounded like. When I turned it all the way back up it was fixed! Loud and clear audio was coming through my Bluetooth ear buds.
I never would have guessed that the call volume for anything would be in the settings for Music but they were. Part of my problem may have also been that I uninstalled the Music app from my iPhone. My music library lived in Google-land since 2010 so I didn't want to convert. I also didn't want the Apple Music app starting up and playing that stupid U2 album that was forced on all of us any time I pushed play on my Bluetooth since it was the only thing I had in that library anyway.
I've had the same thing in the past with screen brightness. It automatically adjusts based on light conditions, but sometimes it would be really bright in a dark place. When I went into Settings > General > Accessibility > Display Accommodations and the turned Auto-Brightness off and on it worked again. That particular problem hasn't shown up for a while now, but it's the same kind of fix.