Is my iPhone compromised?

Some codes can change settings for your phone on your carrier’s network. You need to ask the carrier if you changed anything important. For example, *#62# manages call forwarding for some carriers; people calling your number will be forwarded to a different number. So if you stop getting calls contact your carrier to undo it. And #21# will show the status of call forwarding for some carriers.

Stop following “advice” you get on the Internet or from “helpful” people. It will frequently get you into trouble.

Those are short codes that are carrier specific. You would have to ask your carrier. And what needs to be fixed? And why did you dial a code if you didn’t know what it did?