Postponed number going around vessel's cargo area (2,4)
I believe the answer is:
on hold
'postponed' is the definition.
(I've seen this before)
'number going around vessel's cargo area' is the wordplay.
'number' becomes 'no' (abbreviation for 'number').
'going around' says the letters should be written in reverse.
'vessel's cargo area' becomes 'hold' (area for cargo on a ship).
'no' backwards is 'on'.
'on'+'hold'='ON HOLD'
(Other definitions for on hold that I've seen before include "waiting for reply" , "Postoned, or awaiting reply to phone call" , "Made to wait (on phone)" , "Waiting to be connected" , "Put off" .)