change apple id from phone number to email address

You cannot. If your Apple ID is a phone number, it can only be changed to a different phone number but not to an email address:

From the support document you posted from:

If your Apple ID is a phone number

You can change your Apple ID to a different mobile phone number.

Hi! Follow the directions here.

How to change your Apple ID to a different email address

1. Go to appleid.apple.com and sign in.
2. In the Sign-In and Security section, choose Apple ID.
3. Enter the email address that you want to use as your Apple ID.
4. Choose Change Apple ID.
5. If you changed your Apple ID to a third-party email address, check your email for a verification code, then enter the code. Learn what to do if you didn't get the email.
6. If you use services like iCloud or Messages to share with friends and colleagues, sign in to those services with your updated Apple ID.

Then read again -> Related Article > Change your Apple ID