Take the battery out right away , leave the phone open and exposed to air ,
dont lay it flat , put it on edge to allow the water to drain , after a few days
it should dry out , hopefully its not dammaged.

Pour rice - any type will work fine - into a large container and place the phone beneath the top layer. In a few hours shift the rice and phone so that fresh layers of rice encase the phone. Repeat every few hours for the first day. After the first 24 hours check the phone for moisture inside of the screen. If you still see some then place the phone back into the rice and wait another 24 hours or so. Check again. When it appears to be dry, turn it on and test it. If it's still not working right then turn it off promptly and place it back in the rice for another 24 hours.

If it never seems to function fully again then something was permanently damaged by the water and you'll need to get a new phone - or make do depending on what the damage is.