You can block any number that has called you. You cannot block unknown or private numbers unless you contact your carrier.
 This will show all of the calls you have recently received.
 A menu will appear after a moment.
 The number will be added to your block list.You can see a list of your blocked calls by tapping the "..." button in the Phone app and selecting "blocked calls."

, Your carrier will have much more sophisticated blocking options than you have on your phone. Call the Customer Service line to see what blocking options are available for your plan.
Open the Phone app.
Swipe to the History page.
Press and hold the number you want to block.
Tap "Block number.",
Contact your carrier for more blocking tools.
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