iPhone Microphone Issues - works on camera and Siri, but not on calls

Hello,

I have a similar issue to someone else on here, the microphones on my iPhone 8 only appears to work while doing specific things - the microphone works fine with Siri, Front and Rear facing video, but doesn’t work for calls on both speaker and earpiece, pretty sure FaceTime & voice memos records a flat line and plays a cracking sound. I am thinking it is the bottom microphone that isn’t working, and am hoping it is not logic board. 

As for history; the screen and back are cracked (bought it like this) particularly near the dock section on the back. However, everything else works fine (as far as I can tell) and I opened the phone up and all water damage indicators are white and the phone is mostly clean with little dust.

Has anyone found a solution yet? I have ordered a new replacement housing with parts so it comes with a new dock connector and mic so I will see if that works!