Caller ID is always enabled.
If the incoming call sends its number, the phone will show you the calling number unless that number is in the phone book.
If the incoming number is in the phone book the phone will show you the name of that contact.
You can read the caller ID before deciding whether or not to take the call.
The VX3200 doesn't have any feature to automatically reject specific incoming numbers, but there can be some ways to work around that -- depending on exactly what you need.