Stage of a plan (5)
I believe the answer is:
phase
'stage of a plan' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for phase that I've seen before include "Period within process" , "A particular point in the time of a cycle" , "Distinct stage" , "Period or stage in a process of change" , "Distinct period in development" .)