I got a verification code on iPhone when I didn't ask for it

Someone may be attempting to log into one of your online accounts, which is sending a verification code that needs to be entered to complete the login Your phone has not been hacked.

No. One of your online account passwords may have been compromised, though.

Sorry, I'm not psychic... something sent you a verification code though, so it must be one you have set up for 2 factor authentication.