Popular barrister to sum up (2,5)
I believe the answer is:
in brief
'sum up' is the definition.
(I've seen this before)
'popular barrister' is the wordplay.
'popular' becomes 'in'.
'barrister' becomes 'brief' (I've seen this before).
'in'+'brief'='IN BRIEF'
'to' acts as a link.
(Other definitions for in brief that I've seen before include "skip a lot" , "Taking just a few words" , "Where barrister finds the facts" , "quickly" , "To sum up" .)