When I make calls, people complain of not hearing me. When I speak, the audio output fluctuates
My wife’s iPhone 11’s audio output is bad especially when using the phone for calls ok speakers
Welcome to the Apple Support Communities.
Restart your iPhone - Apple Support and make sure iOS is up-to-date: Update iOS on iPhone - Apple Support.
Then, see: If the microphones on your iPhone aren't working - Apple Support.
If you need more help, contact Apple Support.
Jack
