Why have I got a completely black screen when I press the phone app

[iMore Question]

I had just followed your instructions on how to assign photos to contacts on my iphone, and it had worked, when a short time later I discovered that when I pressed the phone app to make a phone call, all I got was a completely black screen. I tried several times but all to no avail. I have also noticed that the voicemail icon from the bottom of the screen has vanished. Can anyone help me to fix these things. Thanking you in anticipation JM

 

[Just_Me_D]

Reboot your iPhone.