Vibration button isn’t working

You would need to contact Apple Support regarding warranty repair as they do not check the forums. However, have you tried restarting your phone? Verify that Vibrate has been enabled by going into settings>Sounds and Haptics. Also go into General>Accessibility>Vibration and verify that it is on. If that doesn't work backup your phone and do a reset of all settings to verify if it works or not after a reset. If it does do another reset and then restore from your backup.

Call Apple Store and make appointment for them to examine your iPhone They will be best placed to assist you