Telephone Keypad Stuck at Cold Area

I'd dry it thoroughly (eg in an airing cupboard) then give it a squirt of contact cleaner.

Codey

... and in future, try to keep it dry (food storage bags with seals are pretty good) and (if possible) warm.

Need more info. Is this a commercial or private use? Land line or cell? Inside or outside? Pay phones are probably engineered for extreme service, check them out.