how to change apple id

See Use your mobile phone number as your AppleID https://support.apple.com/en-us/HT207944. This document says "depending on the country or region that you live in and how you created your Apple ID, you might be able to change your Apple ID to a different mobile phone number from your Apple ID account page or on your iPhone, iPad, or iPod touch." But, I have never been able to find support for the idea you can change an Apple ID mobile phone number to an email address. I have searched on this topic several times. You can contact Apple Support to see if doing so is possible.

Get a call from Apple support to help solve your problem using this

link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

Apple ID Support https://support.apple.com/apple-id

Apple ID account security for country-specific and

region-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option.}

Based on the article below, I'm not sure you can do that. From the article below.

If your Apple ID is a phone number

If you created your Apple ID with your phone number* as your username on iOS 11 or later, see how to change to a different mobile phone number.

Apple ID Name Change.        

 What to do after you change your Apple ID or password - Apple Support    I suggest doing this before you change your Apple ID or password.