How do I fix this? It was fine up until a couple of days ago and everything was working. Should I bring it into an Apple store?
Apple Support has this to say:
Fix common issues
Follow these steps, testing after each with Voice Memos.
- Unplug anything plugged into the headset jack.
- If you're on a call and holding your phone next to your ear, speak into the microphone and make sure you don't block it with your fingers or shoulder.
- If you're using a screen protector or case that covers the microphone, remove it. Clear any debris from the microphones.
- Restart your device.
- Update to the latest version of iOS.
The mic used for normal calls is the bottom one, check for debris and remove it carefully. There is a membrane between the mic and the phone internals, be careful not to puncture it.
Couldn't find a better pic, sorry.
There are two more microphones, one beside the camera on the back and other near the speaker on top iPhone the phone, they are used for videos and noise canceling; clean them carefully too.