Open the Phone app
Go to Call history or Recent calls
Select the number you want to block
Open the menu or options
Tap Block number or Add to blacklist
Confirm the block
If Block number is not available, open Contacts
Save the number as a contact
Open the contact
Choose Block or Add to blacklist from options
To unblock, open the blocked list in Phone settings or call settings
Select the number
Tap Unblock or Remove from blacklist