Access "Settings" > "Sounds & Haptics".
Adjust the volume to a suitable level. Toggle both "Vibrate on Ring" and "Vibrate on Silent" to the green "ON" position.
NOTE: Check if your iPhone's Mute Switch is on or off. This switch can be used to silence your phone to prevent disturbance. If accidentally left on the "Silent" position it will override any settings and your phone will not ring or alert you with notification sounds.