water dammage

The phone is not supposed to be waterproof; it is water and dust resistant, but but the warranty does not cover water damage. If you purchased AppleCare+ when you got the phone Apple will repair or replace it for $99. Here is more information→iPhone Repair - Official Apple Support

It doesn’t matter how it happened. Put the phone in a dry location, powered down, and let it dry out For a few days. It may recover. But don’t use it or turn it on to avoid additional damage.