Can I get a notification on my iPhone when I receive a certain email?
It is not possible on your iPhone. I searched for a bit if there was a third party email application which had this feature.

If I where you I would look into IFTTT (If This Then That). I'm on my phone now so could not try if you could read body text from emails. But there is a trigger->action: Get a notification when you get a new email with a specific label.

I'm not a Gmail user, but I guess you can make rules. 


Make a rule that looks for incoming mail and scan for the subject or text in body and apply that label to that new email message. 
Make a trigger->action in IFTTT. Let IFTTT watch your Gmail for any new messages with that specific label. IFTTT wil send you a push notification.