Mic not working after screen replacement

Try a phone call and see if you sound muffled or faint. Shoot a video using the front camera and check for sound quality. Them shoot a video using the rear camera and check for sound quality. If those are good and it is just affecting calls and voice recordings then it is likely a matter of the bottom mic got misaligned or has dirt or something stuffed in the small hole. Make sure there aren't any stickers in the way, no dirt or other debris and most importantly it is aligned up perfectly with the mesh and little plastic piece inside. You'll want to remove the screen for that. If it's a different mic then it's probably a matter of the little gold's contacts not limit up right. Alternatively a flex cable could have been folded too sharp or it might need a replacement bottom mic or dock. Also try hard resetting the phone (holding down home and power buttons for 10-15 seconds), go to settings, general, reset all settings, and update to newest ios. to cover software issues. this helps.