I read about wet phones the other day but can't find the site just now.
However, you remove the battery and sim card.
If the water was dirty or salty, rinse the phone in clean water to remove the salt.
Shake and dab to remove the excess water and then put the damp phone in a jar if dry rice for 24/48 hours which should absorb the remaining water.
Replace the sim card and battery and test.
Fingers crossed, it shuld now be OK.
In the meantime I shall carry on looking for the site.
Best of luck.