Before Fixing A Black Phone Screen 
Fixing a black iPhone screen takes some understanding and realization. Since screens play a vital role on your phone, but of course, so you need to be extra careful in your moves.
First thing is that you need to know whether your iPhone LCD cable has become dislodged from the logic board or if the LCD is broken before doing your next move. 
📲If the LCD cable has become dislodged, the Genius Bar at an Apple Store may repair it free of charge, even if your iPhone is out of warranty. That’s because the fix is relatively simple: They’ll open your iPhone and reconnect the digitizer cable to the logic board.  

📲Whereas, if the LCD is broken, that’s another story. It can be very expensive to repair your iPhone display, especially if you go through Apple. Try to do some research or look for a high-quality, less-expensive alternative repair service that will meet you and fix your iPhone on the spot. 
Just an advice, before you do some actions about your iPhone screens, make sure what you're doing is right. Too less your effort and money as well.