iPhone 11 call volume very low
When I use my iPhone's built in speaker to make or receive a call, the volume is very low. It works fine on "speaker phone" and in the car using Blue Tooth. I have tried to adjust the volume during the call and the increase is barely perceptible. I have tried to reboot the phone with no effect. I have tried to toggle the mute button (I keep the mute off) with no success. I have tried toggling the "switches in "Sounds and Haptics" in Settings and no success. Does anyone have any ideas, or should I just go to Apple Store?
iMac, OS X 10.11