Wire is very misleading!  
Anyone only trying to install it on a cell would assume a phone number was required because the “create an account” page in the app only gives that option.  
It was only because you said Wire didn’t need a phone number that I bothered to install it on my PC where the “create an account” page allowed me the option of using an email address instead (which I could then use to log in on my cell). Who designs these things?