> OpenAI cannot tell you if a message is spam, sorry, unless your prompt engineering skills are much better than mine.

Sometimes an e-mail message itself does not even contain enough information to accurately classify it as spam or phish. To a degree, spam is subjective. And classifying a phish may not be trivial at all (e.g. message may include legit marketing links, open redirects and server side logic to serve certain pages only to targets, etc.).