My call volume seemed low on my s8 @rock_roll_5 until I realised it was controlled by turning up the volume whilst in a call.
Some people have had issues caused by cases , screen protectors and debris or lint in the mic port. Network connection / signal can cause certain issues too.
A Samsung Experience Store or Samsung Service Location can run a diagnostic on it.
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help.