How do I block a number from calling me on Talk?
There is currently a beta regarding this functionality: Zendesk Talk beta - Call Blocking. The forum is meant for questions, answers, and documentation around the call blocking beta.
Outside of the beta, it is not possible to block numbers on Talk. Even if you suspend a user, this will only affect requests tied to their email address.
As an alternative workaround, you can rename any users or phone numbers you need to stop calls from to something like "BLOCKED USER - Firstname Lastname” so agents know not to accept calls from that number.