Stop walking briefly to collect gear (4,2,2)
I believe the answer is:
pack it in
'stop' is the definition.
(I've seen this before)
'walking briefly to collect gear' is the wordplay.
'walking' becomes 'pacing' (pacing is a kind of walking).
'briefly' means to remove the last letter.
'to collect' is an insertion indicator (inserted letters are collected by others).
'gear' becomes 'kit' (kit is a kind of gear).
'pacing' with its final letter taken off is 'pacin'.
'pacin' placed around 'kit' is 'PACK IT IN'.
(Other definitions for pack it in that I've seen before include "Give over" , "Slangily, stop doing it - stuff suitcase" , "Quit" , "Stop working - or stuff suitcase?" , "How will you get all that stuff into your suitcase" .)