You need to verify your phone number in order to use SMS Two-Factor Authentication (2FA). Tap here to know how to verify your phone number.
To enable “SMS Two-Factor Authentication, you need to tap near "Enable 2FA via SMS" on the Settings page. Then, you will be asked to enter a one-time “six-digit code” that was sent to your phone.
When you receive the code, input it on the screen and tap “Enable 2FA”.
If you did not get the code on your mobile phone, please tap “I didn't receive the code” (once every 20 seconds).
Each time you log in you will be required to enter a one-time passcode sent to your phone.