A few heard leading review (3,2)
I believe the answer is:
sum up
'review' is the definition.
(thesaurus)
'a few heard leading' is the wordplay.
'a few' becomes 'some' (both can mean a small amount of something).
'heard' indicates a 'sounds like' (homophone) clue.
'leading' becomes 'up' (similar in meaning).
'some' sounds like 'sum'.
'sum'+'up'='SUM UP'
(Other definitions for sum up that I've seen before include "What a judge may do" , "Summarise" , "Make final precis of evidence" , "Review evidence at end of a case" , "Recapitulate (in court)" .)