Perhaps Tommy Cooper's floundering with idea for trick, ultimately (4,5)
I believe the answer is:
rock opera
'perhaps tommy' is the definition.
(work by The Who)
'cooper's floundering with idea for trick ultimately' is the wordplay.
'floundering with' is an anagram indicator.
'ultimately' says to take the final letters.
The final letters of 'idea for trick' are 'ark'.
'cooper' anagrammed with 'ark' makes 'ROCK OPERA'.
(Other definitions for rock opera that I've seen before include "Show" , "Tommy, for example" .)