It has a user name and password for access. The phone number verification is an unneccessary process.
But just to be sure I have changed my number to my UK phone now I am home. To my surprise, the confirmation SMS arrived. I doubt they have fixed the main bug in account setup (which has been reported many times by lots of users) but it did seem to make a change after I got home.

Having said that, the experience of twice being "blocked" at the point of needing a cab probably means that Cabify will be my last choice in any country.