Below are some solutions to iPhone black screen which you can try:
Maybe it’s because your iPhone is out of battery. If so, please charge your iPhone. Usually, you will need to wait until iPhone battery has been charged for 5% or more, then you can try to turn on your phone.
If the battery is not the problem, maybe your iPhone system goes wrong. Try to press Home and Power buttons simultaneously to see if it can lighten up the screen. If not, press them for several seconds to shut down the phone.
If this problem occurs when you are using an app, then it’s probably because the app is stuck. Press Home button for 6 to 8 seconds to exit the app.
If the above solutions cannot help, you can use Phone Manager program to restart your iPhone.