Why does my screen flash but not turn on?

I went to the pool and had forgotten to take out my phone from my pocket since I was holding two other peoples phones it did not occur to me that phone was still in my pocket. I then had jumped into the pool (3 feet deep) and found it in my pocket 5 minutes later. I then left it dry for the rest of the day but when I tried to turn it on the next day the phone turns on but the screen only flashes but does not turn on completely. You can see that the screen is still displaying everything on it but it just flashes that for a second and goes black again but can still swipe to unlock the phone use all the apps and other thinks on the screen but the screen wont display it. Anyone know whats wrong with it?