Actually @danielle I really think this should be decided by the hub! For exemple, one of our users in France uses OFN alongside with a self-service shop in a coworking space. People help themselves in what is stored and fill in what they have taken in the OFN shopfront. In that case you don’t need any phone number as well 
I think for our subsidiarity principle, what is compulsory info or not should be leaved to the hub manager to decide when they set up their hub…