If your phone was fully submerged for any amount of time, it is likely some of the internal components corroded. Corrosion looks like a white, chalky film covering metallic surfaces, and is especially prevalent on pins and connectors that carry current. Corrosion dissolves metals and will cause malfunctions in your phone.

Inspect the logic board and any connectors for signs of corrosion, especially in areas where the LCIs are red.

Check any external ports (charging port, headphone jack, SIM card slot, etc.) for corrosion as well. These may have to be cleaned out with alcohol and a brush, or replaced if cleaning is not practical.

If all LCIs are white, and there is no moisture or corrosion, leave the phone disassembled in a warm, dry place for a day or two to make sure any potentially trapped liquid evaporates, then reassemble the phone.

If any LCIs are red, if there is corrosion or other liquid residue, if the phone fell into dirty/acidic/sticky liquid, or if you just want to be safe, continue for more thorough cleaning.