Turn of phrase used in papers over in Isle of Man (5)
I believe the answer is:
idiom
'turn of phrase' is the definition.
(I've seen this in another clue)
'papers over in isle of man' is the wordplay.
'papers' becomes 'ID' (identifying documents are one's 'papers').
'over' says the letters should be written in reverse.
'in' is an insertion indicator.
'isle of man' becomes 'iom'.
'id' in reverse letter order is 'di'.
'di' going within 'iom' is 'IDIOM'.
'used in' is the link.
(Other definitions for idiom that I've seen before include "Language used by group, parlance" , "Form or variety of language" , "Colloquialism" , "Eg, over the moon" , "Phrase such as over the moon" .)