How do I input a phone number to block without entering them as a "contact?"

Is there a way to simply manually enter a phone number that I would like to block without entering them as a contact?

Also, why is it not possible to completely block a number from being able to leave a voicemail with the iPhone independent of third party applications? It makes no sense to me that we are not able to do this or prevent them from being able to leave voicemails.

Also, I have opted to mute notifications for a few group text message chains, but the only thing that this does is prevent notification sounds/vibrations and not badge notifications which also makes no sense to me. How do I completely prevent notifications for specific group message chains since iPhone has opted to prevent users from being able to remove themselves from group messages? yet another unexplained limitation imposed by Apple.