Phones crash really often. Thankfully, it’s an easy issue to fix.
To reboot an iPhone, hold the power button and home button down until the screen flashes off. Keep holding until the Apple logo appears on the screen.
Press and hold the power button and the volume down button until the screen appears to reset itself.
Hold the power button down until the phone begins to restart.
Press and hold the power and volume up buttons for at least 10 seconds until the phone restarts.