so sad...so gross...
Theres probably corrosion on the connector for the touchscreen to the "main board" (only board) if not in other places.
Disassembly is not that difficult (have to be slightly "handy") and you might be able to clean crud off the connections/legs of ic's.
Ideally for this job you would want a microscope (magnification of some sort), dental picks, alcohol, qtips, compressed air, and deoxit (and of course the torx driver)
If not too much water has gotten in you should be able to clean it. There is a chance you have corroded off traces on the board, or shorted some components...then youre kinda screwed (unless you know how to fix such things which im guessing you dont or you wouldnt be writing here).
But then you end up with a phone that you put near your mouth that you have no doubt "did a number on" which for me would be a little too gross to handle.
If it ain't broke, break it.