Nutmeg's raised pounds in contest — it's phenomenal (7)
I believe the answer is:
miracle
'it's phenomenal' is the definition.
(a miracle is phenomenal or amazing)
'nutmeg's raised pounds in contest' is the wordplay.
'nutmeg's' becomes 'I'm' (where the crossword setter is 'Nutmeg').
'raised' is a reversal indicator (going up in a down clue).
'pounds' becomes 'L' (abbreviation e.g. Lsd - pounds, shillings, pence).
'in' indicates putting letters inside.
'contest' becomes 'race' (race is a kind of contest).
'im' in reverse letter order is 'mi'.
'l' put inside 'race' is 'racle'.
'mi'+'racle'='MIRACLE'
(Other definitions for miracle that I've seen before include "Extraordinary event" , "Remarkable and welcome event" , "Reclaim (anag) - supernatural act" , "Amazing or unexplained occurrence" , "Marvellous thing" .)