Turn of phrase in papers on Isle of Man (5)
I believe the answer is:
idiom
'turn of phrase' is the definition.
'papers on isle of man' is the wordplay.
'papers' becomes 'id' (identification papers).
'on' means one lot of letters go next to another.
'isle of man' becomes 'iom'.
'id'+'iom'='IDIOM'
'in' acts as a link.
(Other definitions for idiom that I've seen before include "Phrase with a meaning that is not literal" , "Artistic style" , "Characteristic style of expression" , "Dialect, vernacular" , "Use of words" .)