I know this my sound silly, but sometimes the outside volume buttons will activate the media/ring volume, while the call volume itself is all the way down. I’ve done this myself where I accidently thought I was lowering the media/ringer volume & lowered the call volume.
Also, who is your network provider. Sometime, this could be carrier related.
@urszula Thanks for your quick reply! I’ve got the call volume all the way up. I’m with AT&T, but I saw notes from others that it didn’t improve when switching carriers. I am also noticing that media volume and ring volume get so much louder than call volume. So the phone hardware is capable, but this makes me wonder if it’s a software limitation.
I keep having this issue either with MK Global version. Sometimes it’s fair, sometimes e.g. I have to keep it close to my ear despite loudspeaker. Always making sure call volume is all the way up. Must be some other volume slider or another hidden value < 1.0 that affects this.