Simply go to your list of recent callers (open the Phone app, then hit the Recents tab at the bottom). Click the 'i' symbol next to the unwanted number, scroll down and tap Block this Caller, then confirm your decision.
Simply go to your list of recent callers (open the Phone app, then hit the Recents tab at the bottom). Click the 'i' symbol next to the unwanted number, scroll down and tap Block this Caller, then confirm your decision.