iPhone water damage, touch screen issue

Sorry to disappoint you but the "rice thing" does nothing to help your phone and causes more damage than it solves.

The water is inside the phone, on the logic board and under the shields, even under the IC's. The rice is nowhere near where the water is. So while it may soak up some water vapour, the real problem is the corrosion that is taking place as the water evaporates. Powering on the phone accelerates the process. The longer you let a phone sit in rice, the more time you are giving corrosion to damage your logic board. The saltier or harder the water is, the more damage will occur.

In your specific case, the logic board is probably damaged, specifically the backlight circuit. This requires a micro-soldering repair and is not a DIY fix. You could try the following to see if it helps:

• Open your phone and remove the logic board (follow this guide)
• 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.
• Re-assemble and hope for the best.