Here in the identity division at Microsoft, we don’t like passwords any more than you do! So we’ve been hard at work creating a modern way to sign in that doesn’t require upper and lowercase letters, numbers, a special character, and your favorite emoji. And after a soft launch last month, we’re excited to announce the GA our newest sign-in feature: phone sign-in for Microsoft accounts!

https://blogs.technet.microsoft.com/enterprisemobility/2017/04/18/no-password-phone-sign-in-for-microsoft-accounts/