1. Go to the settings menu on your iPhone.
2. Click on "Password and Accounts".
If you're on iOS14 or later, your settings will be a little different. You'll have to go to Mail > Accounts
3. Click on your email account, example "Exchange".
4. Scroll down and click on “Delete Account”.
5. On the next screen confirm deleting your account, click on "Delete from my iPhone" to finish.