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.
Press and hold the Power/Lock Key 
on the right side of
the phone, 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 sound mode icons to switch to that mode.
OR
Press the down Volume Key 
on the left side of
the phone until Silent mode is displayed.
OR
Open the Notifications panel and tap the Sound icon until Silent 
is displayed.