We’d like to simplify the sign-up process on the web. It contains two pieces - retrieving the user ID and verifying it. The v1 is concentrating on the phone numbers as an ID.
Currently the sign-up process is cumbersome especially on mobile. The user may have to type his phone number, submit the form, wait for the SMS and open it, copy the OTP, switch back to the browser, paste the OTP and submit the form again. With the help of a browser the same process may require just one click and no typing at all. In addition to that the verification part can be useful in other scenarios. For example, user wants to conduct an online transaction and the bank/merchant sends an OTP via SMS for better security.
The explainer doc covers the motivation and a possible approach.