SE volume poor on phone calls

When making phone calls, incoming volume is quite low, very hard to hear in noisy backgrounds. Max volume does not help; the sound itself is still quiet.

Other volume is all fine: music, speakerphone function, headphones, etc.—but that's a different speaker, right?

Can't tell if this is a software or a hardware function. But is the speaker above the screen used for anything besides phone calls so we could test it?

Has anyone else run into this, and if so what was the resolution?