One new phrase about fabulous monsters (7)

I believe the answer is:

harpies

I'm a little stuck... Click here to teach me more about this clue!

'fabulous monsters' is the definition.
'harpies' can be an answer for 'monsters' (I've seen this before). I'm not certain of the 'fabulous' bit.

'one new phrase about' is the wordplay.
'one' becomes 'i' (Roman numeral).
'new' indicates an anagram.
'about' is an insertion indicator.
'phrase' with letters rearranged gives 'harpes'.
'i' inserted inside 'harpes' is 'HARPIES'.

Can you help me to learn more?

(Another definition for harpies that I've seen is " monsters".)

I've seen this clue in The Globe and Mail.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.