According to the "laws" of separating business logic and presentational logic (i.e. controllers/blocks/templates), it would be better to put logic in the Block class, and only use display logic in the templates/views.
But since this is simply a single variable you retrieve from the backend, I think you can just use:
in your template.
There are exceptions however, for example imagine that the phone number would contain a comma separated list, it would be better to extract the phonenumbers in the Block than in the template, because that's easier to maintain.