Reset your iPhone
Issue
Your iPhone is becoming unresponsive, the screen is fading away or it's not responding to any external button pressed or it's not accepting any screen taps.
Solution
Here below is a simple method how to reset your iPhone (note that's it's not the same thing as Restoring to its factory settings where all data on your is cleared), consider it as if you were restarting your iPhone from fresh.
Press and hold down the
Sleep/Wake button and
Home button simultaneously for a least 10 seconds the screen will clear out and then the Apple Logo will appear on the black background. When the logo appears it means that reset is done.