Yeah, your phone is bricked. Happened before when I jailbroke and fucked my iPhone 5 up. Never heard of it bricking for an update /: if you can't fix it within a day or so consult the store and if they don't do shit consult Apple. I was going to say do the lock and home screen but I guess not now. The only other thing I can think of is look up a YouTube video fe: How to fix iPhone 6 black screen on update. blah blah blah. Sorry I couldn't help you but i went through the same process before, had to do some funky shit in iTunes but it worked. The best of luck to you my friend, hope it gets working.
------
If I'm a dumbass and there is a way to fix it simple look around, ask people who know more and have a better understanding of technology than me. other than that, YouTube is your best second guess.