Sign in to your Account Info page.
Click Account security.
Click Add recovery phone number.
– A pop-up window opens.
If you already have a phone number set for your account, click the existing phone number.
Enter the mobile number you’d like to use in the field provided
If you’re adding a second mobile number, click Add recovery phone number.
Click Send SMS or Call me.
Enter the SMS verification code you were sent.
All set! Make sure you enter your SMS verification code so that we can use it to confirm your identity if you run into trouble.
If you don’t receive your message within 24 hours, it’s ok – you don’t need to request a new one, but you may need to perform some extra steps form our verification help article.
Or you can contact yahoo customer service.