How do I silence the iPhone ringer / enter vibrate mode?
The iPhone can be silenced with one switch. The upper left hand corner of the iPhone has two volume buttons and a sliding switch. This sliding switch is the ring/silent switch. To place the iPhone in vibrate mode and silence the call ringer flip the ring/silent switch down so that a bright orange color appears. The iPhone is now in silent mode.
Vibration can be turned off when in silent mode. To turn off vibration, navigate to Settings -> Sounds & Haptics -> Vibrate on Silent -> OFF (grey slider)