@Andy0121: To troubleshoot the issue, please double check that the feature is active by heading to Settings > Advanced features > Motions and gestures > Alert when phone picked up, and toggle this option on. If the feature is enabled then, next time you miss a call, please can you check to see if the phone vibrates when its idle/locked? For reference, the alert will only function if you have a corresponding missed call notification on the Lock Screen or Always On Display.
