Confirming your phone number is optional but recommended for several reasons. When you confirm your phone number, you can quickly set up 2-Step Verification for added account security. You can also use it as another method to reset your password or recover your username.
If you do not want to confirm your phone number, you can choose “Remind Me at Next Login” to skip it for this session, or “Don’t Ask Me Again” to not receive this prompt again in future sessions.