You must pass in the body mail or phone number along with the + sign
Examples:

1. myregmail@gmail.com
2. +447721436050

Mostly safetynet is used when registering accounts, but it can also be used for authorization.

In other words, when you register, you give what you are registering for (email or phone_number).
And when authorizing, what you are authorizing with(email or phone number).