If your iPhone rings but doesn't vibrate when someone tries to call you, it's possible that the Vibrate on Ring option is disabled. Follow the below-mentioned steps in order to enable this option:
Go to Settings and select Sounds. Move the slider next to Vibrate on Ring to the right.
Maybe you have accidentally turned off your mobile device. If this is the case, all you have to do is to turn on your mobile device.
Maybe the vibrator got stuck. A gentle tap on the back of the device should be enough to unstuck it.
If your iPhone doesn't vibrate nor ring, but you receive notifications in your voicemail when somebody calls you, it's possible that you have enabled the Do Not Disturb mode. If you see a half-moon icon next to the battery icon (in the upper-right part of the screen), this option is enabled.
You can disable this mode either via the Action Center or via Settings:
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.