People can’t hear me on calls, or FaceTime etc

Hello,

2 questions:

• Are you using headphones? And if you are have you tried switching them out?
• Have you tried blowing out (GENTLY) the speakers with some air?

To remove the dirt in the microphone:

1. Open some compressed air
2. Blow it at the grill on the top
3. Blow into the bottom left microphone
4. Blow into the mic at back on the right of the camera
5. Most of the dirt should be gone so people should hear you

Another possibility is in your microphone privacy settings:

• To turn on your iPhone’s microphone, go to Settings > Privacy > Microphone > make sure the app you’re using for calls if toggled on.

Another possibility (very rarely) is your network settings try this to reset your network settings:

1. From the home screen, tap Settings
2. Scroll down to, then tap General
3. Scroll down to, then tap Reset
4. Tap Reset Network Settings
5. Tap Reset Network Settings to confirm

You can also try to force reboot your iPhone and that may help your situation:

Comment forcer le redémarrage de l'iPhone 8

Lastly you may need to replace your speaker if all else fails:

iPhone 8 Troubleshooting

iPhone 8 Earpiece Speaker Replacement

Good luck!