When you experience distorted or no sound during a phone call, it's a clear indication that there is an issue with your earpiece. Although it could potentially be a software problem, it's more probable that you will need to have the earpiece repaired or replaced on your phone.
If the sound is coming through but it is vary faint try cleaning the ear speaker mesh ( old toothbrush is a good DIY tool ) can work magic.
While you may not be able to hear phone conversations through the ear speaker, you should still be able to listen to music on your device using either the loudspeaker or earphones. To get a thorough diagnosis of any issues and a breakdown of necessary repairs and costs, bring your device into Hex's Edinburgh store.
Hex - Edinburgh's Professional iPhone Repairs , Open 7 Days a Week
Visit us at 14 Home Street,Edinburgh
or give us a call 0131 221 1117.