Is it fixable?(water damaged iPhone 6)

I have an iPhone 6 that was dropped in a lake. For about a week it was just a dead phone and didn't even accept a charge. Then after a week the phone came on and could accept a charge. The phone has an image but it is very blurry and it is hard to make out anything on the screen. I thought that was the only piece i would need replaced and it now has a new screen with a clear image. The only problem is that the touch screen does not work. The person who fixed my iPhone told me i would need a new mother board. Would this work? and is there an easier fix?