Look into the lower mic hole with a bright light. If you keep the phone in a pocket, it can pick up lint, which gets jammed into that hole - and lint is a good sound insulator. Use a thin, pointed, wooden toothpick to pull the lint out.
If there's no lint in it, the mic probably went bad and has to be replaced. (The ridiculous price is for taking the phone apart, then gluing it back together. Even if they replace the whole board that the mic is on, it's only about US$10. [The mic itself is probably a few cents.])
12-22-2018 01:24 PM