Hardware key control mode
If your phone display is damaged or broken, you can answer an incoming call, end a call, or turn off an alarm using the hardware keys.
Turn your phone off.
Press and hold the Power/Lock Key
and the Volume
Keys 
at
the same time for more than 6 seconds to enter the Hardware key control
mode.Press the Volume Keys
to scroll to the desired
option, then press the Power/Lock Key to confirm.Answer a call: Press the Volume Keys at the same time.
End a call: Press the Power/Lock Key during a call.
Stop an alarm: When an alarm rings, press and hold the Volume Up Key or Volume Down Key to stop the alarm. Press once to snooze the alarm.
If you use your phone with a broken display glass, your phone can break even more or you can be injured. Make sure to visit the LG authorized service center to get your phone repaired.