When it come to liquid damage, it’s always best not to turn the phone on until it been opened and the boards been treated. If it sat in water for 4 hours you probably have some corrosion already building up on your board, which will definitely cause various components to stop working. I’d back up anything important and have the phone looked at professionally. J3’s are tough normally retailing for around $200 it may be more cost effective to replace the phone as water damage repairs can sometimes be very expensive. Best of luck!