Even if Vibrate on Ring and Vibrate on Silent are turned on, your iPhone won't vibrate if your ringtone's vibration pattern is turned off.
How Do I Make Sure Ringtone Vibration Is Turned On?
- Open up the Settings app.
- Scroll down and tap Sounds & Haptics.
- Under the Sounds And Vibration Patterns submenu, tap Ringtone.
- Tap Vibration.
- Make sure the vibration pattern is set to anything but None.
- The vibration pattern you have selected will have a small check mark next to it.