You can block up to five numbers for free through your MyVerizon account on a computer.
Login to your MyVerizon account. Then after the "I want to..." section click on the "Block Calls & Messages" box in the Plan column.
In the next screen on the "Call & Message Blocking, add the ten digit phone number in one of the slots and click on the "Submit" button. When it is processed, you will get a confirmation dialog box saying that "Your changes have been saved. Call & Message Blocking successfully updated." with an "OK button.
If you need to permanently block a number then you need to subscribe to their "Usage Controls" which has a monthly fee.