Turn of phrase in papers I'm carrying round (5)
I believe the answer is:
idiom
'turn of phrase' is the definition.
(I've seen this in another clue)
'papers i'm carrying round' is the wordplay.
'papers' becomes 'ID' (identification papers).
'carrying' indicates putting letters inside.
'round' becomes 'o' (round can mean a round object).
'im' placed around 'o' is 'iom'.
'id'+'iom'='IDIOM'
'in' is the link.
(Other definitions for idiom that I've seen before include "Distinctive speech" , "Characteristic language of people or group" , "Colloquial saying" , "Characteristic style, vocabulary" , "Group of words in which the meaning may not be obvious" .)