How can one set iPhone X to Vibrate only ?
How can one set the iPhone X to Vibrate only for incoming calls and messages?
Turn the Ring/Silent switch to silent. See the following for the location and for the excerpt below:
About the buttons and switches on your iPhone, iPad, or iPod touch - Apple Support
Ring/Silent (iPhone only): Use to mute sounds and alerts on your iPhone. If the switch shows orange, it means your iPhone is in silent mode and will vibrate for incoming calls or alerts. When in silent mode, the alarms you set in the Clock app will still sound, and calls from Favorite contacts will still ring.
Also note there is an option at Settings > Sounds & Haptics > Vibrate on Silent that will need to be on.