You must contact your employer and ask to remove the MDM profile so that you can use the iPhone as a private iPhone.
Then log in with your private Apple ID.
If you no longer work for that company, that company has already deleted your work email address. This is done as soon as you have left the company so that you can no longer log in. You no longer have any rights there.
An deleted email address, it is no longer valid, it simply no longer exists and it no longer works.
You may not be able to change that email work address because it is no longer exists.