I can barely hear on a phone call even though the volume is on max

How are you setting the volume to max? The volume control buttons only change the call volume while you are on a call. You cannot change the volume if you are not on a call. On the Home screen they change the ringer volume, if you are in an app (like Music or a game) they change the volume for that app.

Another possible reason is you did not take the film that the phone ships with off the face of the phone.

If neither of these help, make a genius bar appointment to have the phone looked at: Genius Bar Reservation and Apple Support Options - Apple