Article found in minor road in passing (2,3,3)
I believe the answer is:
by the way
'in passing' is the definition.
(I've seen this before)
'article found in minor road' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'found in' indicates putting letters inside.
'minor road' becomes 'byway' (I've seen this before).
'the' put within 'byway' is 'BY THE WAY'.
(Other definitions for by the way that I've seen before include "Where 14's [HARD SHOULDER] situated" , "Where to find kerbstones" , "At the roadside - incidentally" , "Incidentally, as a rather irrelevant comment" , "At the side of the path?" .)