iPhone XR Microphone sounds distorted through calls, voice memos

I've been told by the last few people I called that I sound 'distant' or as though I'm 'underwater', and I'm almost entirely inaudible on speaker phone. Playing back a recording in voice memos sounds heavily distorted, tinny (like a high pass filter), and with lots of background noise. The audio in videos seems fine by comparison (maybe slightly muffled, though still clear).

Which microphone/s are in need of fixing/replacement?