How to fix my submerged phone

Turn off, don't do rice and don't try to charge it.

If you can, the preferable option, would be to take it to a professional who uses a high quality ultrasonic cleaner (not a jewelry cleaner), and cleans it thoroughly.

Make sure the store uses a frequency wave machine such as Crest ultrasonic.

If not buy a small set of tools, disassemble and scrub it lightly with 99% isopropyl alcohol. Let it dry for 30 minutes re examine and test.

Always examine the board first before cleaning in case the cleaning doesn't fix it. That way you know where to look to repair in case if you chose to go further with it.