Since you phone seemingly survived severe water damage I’m surprised it’s even turning on right now.
Steps to take are:
# opening it up
# checking if the battery has bubbled up
# if so remove it carefully!
# dispose it the intended way (be careful it can be prone to “explode” / secure it into something that is fire resistant upon disposal)
# removing every little part from you phone
# drying the !&&* out of it
# checking every little contact for corrosion (especially the circuit boards)
# put everything back together and replace the broken screen on your way out
In my opinion it would be easier to just buy a new one - these things go for cheap on eBay and are easily repairable.
I can’t stress the danger of a shorted battery enough - if it’s getting bigger as you’re handling it throw it the f*** away from you, ideally somewhere where nothing else can catch on and start a fire.