Are you suffering from quiet calls on your iPhone?   The volume slider is at the maximum but calls still come through quiet making it hard to hear the caller?    If so, there may be a simple solution – a screen protector!

If you have the wrong shape, or placement of a screen protector, it might just be covering the headset speaker!   This will only affect calls, as the speakers on the bottom of the phone kick in for other sounds.

Good luck!