The help center defines questions on phishing as on topic here and I personally would agree to that, if this follows the same logic as given by AviD here.
Quote from AviD:
If the question is based around either actual security measures, or business risk analysis...
AND if it's not about your grandmother getting scammed at home... AND if it's not about "help i got phished quick what do i do" AND if its more about "business" security.
I would therefore argue, that the FAQ in the help center should be revised to include the same logic as above and "Is this a phishing mail?" questions should be flagged as off topic from the get go.
Another approach could be the following:
I was looking for good duplicate targets for the duplicate question list and stumbled upon this question.
The answer lists a number of methods to identify phishing and scam mails which is basically the same methods we would apply if a user asks the question "Is this a phishing attempt?"
From now on every "Is this a phishing mail?" question could be marked as a duplicate of this question.