Turn of phrase used in papers Im carrying round (5)
I believe the answer is:
idiom
'turn of phrase' is the definition.
'papers im 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' going around 'o' is 'iom'.
'id'+'iom'='IDIOM'
'used in' is the link.
(Other definitions for idiom that I've seen before include "characteristic use of language" , "Colloquial saying" , "Phrase such as over the moon" , "Language used by group, parlance" , "Distinctive expression" .)