Low quality Apple Music app audio when doing conference calls
Are you using a Bluetooth headset? If so, try the following:

Go to System Preferences → Sound → Input and select a device other than your bluetooth device, for example "MacBook Air Microphone."

Note that if you disconnect your bluetooth device, you might have to do this step over again. Inconvenient, I know.

This is because bluetooth does not have enough bandwidth for 3 audio channels at the same time, so it is either: (1) two speaker channels (stereo) or (2) one speaker channel (mono) and one microphone channel.