How do I remove iCloud account from my iPhone?

To remove an Apple Account from your phone, you tap on it and provide the Password. The iPhone is locked to the Apple Account that is signed into it and the only way to remove it without the Password is to provide the original purchase receipt from Apple or Authorized Apple seller. Apple does not get involved in any third party sales, so a receipt from any other source likely would not be accepted.

• Did you purchase a used phone that is locked to the original owner?
• Is there some other reason why you are unable to remove the account?
• Is there something else you are trying to accomplish?

You can’t. All you can do is not use it.

The All Too Common SAD Reality of Buying a used iPad/iPhone - Apple Community