When I originally fixed the screen on an iPhone 7 plus, the earpiece speaker stopped working. After doing some digging on ifixit i learned that the flex cable that I had moved over is very sensitive and the soldering can microcrack easily. IF YOU READ NOTHING ELSE READ THIS: Make sure you buy quality replacement flex cables from a reputable vendor (aka ifixit) poor soldering on cheap flex cables will lead to the same problems with a non working ear piece.
Easy to replace, Just make sure you have apples proprietary Y-type screwdriver.
USE QUALITY REPLACEMENT PARTS.