I’ve had this problem too. Just today, my German Shepherd knocked my phone out of My hands and it dropped into his water bowl. It worked just fine, up until it was time to change it. It would show the charging symbol for about 3 seconds then go blank. I have an iPhone 6 so this may not apply to everyone. First off, TURN THE PHONE OFF!!! Completely!!! If it is not working, do a hard reset. Then, remove the SIM card. If it has a red color that means there is water damage to the inside of the phone and there is nothing you can do about it. If it is white or grey, that means there is no damage to the inside of the phone and you can proceed to the next step. Put the SIM card back in and turn on the phone. Put it on charger and see if it works. If not, take it to your carriers nearest store to get it fixed.