So to start off with, at least you headphone jack is working and not stuck in headphone mode which can be a P.I.A. I know this is possible because I have a audio jack I take phone calls with with my car and people can hear me through one of the 3 microphones.
1. Let's test to make sure all of your microphones are working. Take two quick video and say test or something on both the front and rear camera. Playback and confirm you have sound.
2. If you haven't deleted it with the new IOS, go into voice memo and click the upper right corner of the screen with the sound icon, it's a little buggy since IOS 10 so toggle it from blue to white a couple of times to make sure its recording on your lower microphone and test the lower microphone by making a recording. If all three of your microphones work than we can go from there.
Let me know the results!