iPhone 5s won't turn on but proximity sensor blinks whenever plugged

My current situation with my iPhone 5s is that it refuses to turn on or charge but whenever it is plugged to my wall socket (but not my computer), the proximity sensor begins to blink rapidly and it lasts for quite a while.

This is how it happened: I brought my phone with me to the beach and sealed it in a supposedly waterproof Otterbox case. I used it in the ocean and submerged it for a few minutes in the water. I was going to take a picture so I got my phone but when I pressed on the home button, I was shocked to find it wouldn't function anymore. I very carefully took my phone out of the case and saw that a little water seeped in but it really seemed like NO cause for worry. I was with my boyfriend at the time and he was inspecting the phone, nothing seemed off, everything was still working except the home button and my screen protector wasn't wet. I thought it was just coincidental that the home button stopped working (since I heard iPhones tend to do that). However around an hour after that incident I noticed my iPhone was heating up abnormally. I allowed it to cool down that night. When I woke up, the battery was drained. I took it to my brother who is pretty tech savvy and told him what happened, asked him if I could charge it. Since we both believe the water probably didn't do anything and we didn't have the tools to open up the phone, we charged it and it seemed to work fine until this line started appearing at the bottom part of the screen. Also, whenever I would press the home button, it would immediately go to Voice Control. A message also kept appearing saying "This cable or accessory is not certified and may not work reliably..." even though nothing was connected. The battery was suddenly draining a lot faster than usual and again, it was heating up. The iTunes logo popped up on my screen so I connected it to my computer. It suggested I update or restore it. Since there were very important pictures and videos I wasn't ready to let go of, I updated it but it didn't do anything. Then the battery died and the logo with the red bar and the lightning bolt signalling me to charge it kept flashing. I tried charging it but it wouldn't work! The phone finally died altogether and now whenever I try to charge it, only the proximity sensor blinks. Tried doing a hard reset but obviously won't work since my home button is busted.

Also, if it helps to know I JUST updated the software to iOS 9.3 before going to the beach.

I haven't taken it to the Apple Shop yet because it's Holy Week here and everything is closed 'til tomorrow. Just wanted some feedback to calm my nerves, Is there anything I can do? Is my phone a goner? I really hope my phone isn't completely fried and it can be restored without resetting it since I have some very sentimental data in here. :(