delete iCloud email account

First of all see what are email accounts and how are they created see these articles https://support.apple.com/guide/icloud/what-is-icloud-mail-mm6b1a17e3/icloud

https://support.apple.com/guide/icloud/set-up-icloud-mail-on-your-devices-mmdd8d1d47/1.0/icloud/1.0

In Mac from mail accounts these accounts can be deleted see the steps in the article https://support.apple.com/en-in/guide/mail/mail35803/mac

The Apple ID and password is signed in system preferences of Mac , the box of mail was checked and it synced with iCloud.com , once you delete the account from mail application of Mac it will be removed from iCloud.com also .

From iPhone , just sign out Apple ID the mail account is removed https://support.apple.com/en-in/HT208242

As in iPhone the mail account is just synced by adding the account https://support.apple.com/en-us/HT201320

And there is no deleting the mail account directly in iphone as if you compare with Mac in the location with mail preferences > accounts .