Just fixed this same problem. I had replaced the lcd screen on an iphone 5 and the earpiece didnt work after. Heres how i fixed it. I went back over all of the ribbon connectors to make sure they are all seated well. That didnt fix it, so i took the earpiece off and cleaned the two copper contacts (attached to camera's ribbon connector that the earpiece prongs make contact with. After cleaning them with my contact cleaner pen i made sure they were properly aligned so they earpiece prongs would be touching them. Then when i went to reassemble i flipped over the 3 ribbon connectors and blew them out to make sure there was no dust or debre hendering there contacts. Reassembled and it worked fine. Not sure which of those three steps did it but you might as well do them all while your in there. Hope it works out for everyone else like it did for me.