'Monger' and 'mongering' aren't words on their own, but occur in compounds like 'coster-monger', 'warmonger'. They imply a merchant, a seller, typically a small seller in a market or on a street. So 'phrase-monger' to me suggests someone is trying to impress you with lots of cheap, flashy phrases. The sentence you quote is a good example.
While etb is correct in suggesting that monger is most often used in compound forms, AE does use it alone to mean peddler or huckster, usually in a disparaging sense. A phrase-monger is one who puts forth phrases—of uncertain quality at best—to excess.
Here is a recent example of monger in standalone use:
This assumption is wrong on so many levels I don't know where to start. It is telling that MSDN has strayed from being where developers get up to speed on existing Microsoft technologies to being a primarily a monger of vaporware.