You can quickly silence your phone.
From the Home screen, press and hold the Power/Lock key (on the right side of the phone), then tap the Silent mode icon .
OR
Press the Down Volume key (on the left side of the phone) until vibration is set, then press it again to turn off all sounds.
OR
Swipe the Status Bar downward to open the Notifications panel, then tap the Sound icon until the Silent icon is displayed.