Your account for Skype enables you to connect with what's important and gives you access to other Microsoft services like OneDrive, Xbox and Office. If you are trying to sign into another Microsoft service, you may be prompted to add a phone number or email address. We do this to ensure that your account is more secure and to make it easier for you to recover your password when necessary.
You may receive the error "Microsoft account already exists. Enter another email or phone, or get a new Outlook email." You will see this message if the email or phone number you are trying to add is already tied to another Microsoft account. You will need to use an alternate phone number, an alternate email or create a new one.