Sea water is one of the worst liquids to get inside a phone, because of all the salt etc. It corrodes extremely quickly, and causes major damage.

I don't know if there is much hope now, but you could try a DIY clean, by dissembling the phone and going over everything with a toothbrush and 99.9% isopropyl alcohol, or go for the more professional approach using an ultrasonic cleaner, maybe a repair shop offers liquid cleaning etc. :-)