Water damaged phone screen lights up green with a cross in the middle

A few months back this phone was thrown into a garden pool (without chlorine). The phone initially worked fine so i thought nothing of it and didn’t dry it right away. Unfortunately after a few hours the phone’s screen went white and turned off. Now when I plug it into my charger all i get is a green screen with a white cross in the middle. Here is a link to “imgur” of how it looks. https://imgur.com/a/GurPLS0

Would putting the motherboard in isopropyl alcohol help? Would changing the screen do the trick? Is the phone beyond repair or still fixable? I have a lot of experience working on PC parts but I never worked on a phone so if the phone is repairable even the smallest and most obvious tips would be appreciated.