Ecstatic to be performing obscure number (2,5,4)
I believe the answer is:
on cloud nine
'ecstatic' is the definition.
(I've seen this in another clue)
'performing obscure number' is the wordplay.
'performing' becomes 'on' (as in being on stage).
'obscure' becomes 'cloud' (cloud can mean to obscure or conceal).
'number' becomes 'nine' (nine is a number).
'on'+'cloud'+'nine'='ON CLOUD NINE'
'to be' acts as a link.
(Other definitions for on cloud nine that I've seen before include "delighted" , "Transported" , "Ecstatic" , "Extremely happy" , "Elated" .)