To turn the phone sounds off
If you’re in a place where your phone sounds may disturb others, you can quickly silence your phone from the Home screen.
From the Home screen, press and hold the Power/Lock
Key 
, then tap the Silent mode icon 
.
NOTE
Only one mode can be selected at a time. The currently activated mode (Silent, Vibration, or Sounds) is underlined in blue. Tap any of the sounds mode icons to switch to that mode.
OR
Press the down Volume Key 
on the left side of the phone until all sounds
are turned off or vibration is set.
OR
Open the Notifications panel and tap the Sound icon 
until is displayed.