Hello
- I would re-open the phone and check it carefully following the waterwiki advice. You mentioned rice which got me worried. Please double check with the source I linked
- You could look for a local Angel/community to test spare parts
- You could run troubleshooting via self-repair portal
- You could purchase spare parts and swap them yourself. I guess you are lucky that FP3 microphones seem to be user-swappable. I would use the 4th step as a last resort.