My phone had dropped in the sink (water damage)

Syed, just like any other electronics that was submerged, the first thing to do is to not turn it on. then you do want to disassemble it all the way. Remove any EMI shields, clean the logic board, connectors and cables with a high grade 90%+ isopropyl and a soft brush. While you are cleaning it, check for any burned, charred looking or missing components. Replace the battery and re-evaluate to see if and what, if any, damage you may still have. The overheating can be caused by a bad battery as well as a shorted PMIC. Hope this helps, good luck.