Microphone only works with headphone in

When making calls, people cannot hear my voice, though they can hear garbled noises coming through. Having headphones in increases the sound quality to the point where I can be heard and understood, but not as clearly as normal.

I have tried using safe mode and the problem was the same. I visited a Cell Phone Repair shop and they quoted me a total of $215 to replace the microphone, because apparently they would have to also replace the screen to do so… so it was two costs (screen and mic), $149 and $65 (I don’t remember which was which, sorry).

The phone is not worth much more than that, so I am trying to find out how much the microphone itself is worth. I would rather try to fix it myself.

Thanks in advance for any help!