You need to do as close to a full decontamination as possible. Your phone was immersed in water for an hour so there will be water everywhere. The water is inside the phone, on the logic board and under the shields, even under the IC's. The real problem is the corrosion that is taking place as the water evaporates. Powering on the phone accelerates the process (oxidation).
Here's what you need to do if you can't bring it to a professional:
- Open your phone and remove the logic board
- Inspect the logic board, especially around the connectors and look for corrosion.
- Inspect both sides of the board. Unfortunately, 80% of the board is covered in shields. That's usually where the damage is occurring.
- Put your board in a container with >90% isopropyl alcohol and let it sit for a while.
- Use a soft brush, like a toothbrush and lightly brush away any corrosion you see.
- Rinse in alcohol and repeat.
- Let it air dry for a day.
- You should also consider getting a new battery as it may have been damaged by water. Li-ion failures are dangerous.
- Re-assemble and hope for the best.
A professional repair shop that does water damage repair may be able to recover your phone or the data because they have access to pro-level ultrasonic baths and specialized cleaners as well as the skills to troubleshoot your board.