2nd reinstall note - make sure the antenna cable (step 17) is routed through the provided slot (back side of speaker assembly). Got mine trapped underneath the first time, looked fine until later in the process.
I was able to fix this when I noticed it at step 18 (the unnamed cable was protruding), by removing the screw at the other end of the cable, which also holds the mic port. This let me wiggle the mic port enough to slide this end underneath without backtracking.
The washer mentioned is part of a cable that wraps around the mic jack, which has to be moved from the original part. The other end is held by the red screw in step 22; when reassembling, just put this end back on top of the speaker assembly after it's back in place.
This cable is attached with an adhesive patch, and required a bit more force than I expected. It is part of the replacement piece, so don’t worry much about damaging it.