BLOCK A CONTACT: From the home screen, select the Phone app. Note: When a call is blocked, it is routed directly to voicemail. The call blocking feature may not affect phone calls made or received via third-party apps installed on your device. Please contact third party app developers for assistance with such applications.
Select and hold the desired contact, then select Block Contact.
UNBLOCK A CONTACT: From the Phone app, select and hold the desired contact then select Unblock Contact.