You didn't clean the inside completely. Some of the impurities left in the phone are causing shorts, corrosion, and are etching through conductors. (Even if the phone is dry, unless it's in 0% humidity nitrogen or carbon dioxide, it's being destroyed slowly.) The phone is pretty much a lost cause, it's just going to keep getting worse until it fails completely.
Repairing it will cost more than replacing it, unless it's a very expensive phone - then you might save a little by having everything in it replaced. (The housing is probably still usable, so if that costs more than the labor, you;ll save the difference - but it won't be as much as $100 for a $700 phone.)
For your future knowledge, in case you get a phone wet again, read
Oh, no! My Phone got Wet!
