In the phone dialer application on recents tab, touch the phone number you want to block to open the mini menu and then touch the "block" option. Be sure to not touch the phone symbol on the far right side of the number line when opening the mini menu as that will cause the phone to dial that number.
Alternatively you can manually add a number to the block list under the Settings > Blocked Numbers in the phone dialer application.
This won't prevent that number from leaving you a voicemail. If you need that functionality, you will need to block them from your MyVerizon account online.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
We understand your concern with blocking calls and we want to help in the best way. Here is a link with more information on blocking calls https://www.verizonwireless.com/support/knowledge-base-200867/ Let us know if this helps?