I have a customer that brought his iPhone 6 saying his ear speaker volume was very low and he could barely hear what the other person was saying even in a quiet room. I did some tests and when I use the recorder to record my voice and listen to it through the ear speaker the sound is crisp and clear, I hear very well.
When I try to make a phone call, the sound is very low, even with the volume at maximum. I tried switching SIM card and even replacing the ear speaker and flex cable.
What could be causing this problem ?