Performing on stage with a common plan? (2,7)
I believe the answer is:
in concert
This clue is a double definition.
'performing on stage' is the first definition.
'with a common plan?' is the second definition.
('in concert' can mean working together)
(Other definitions for in concert that I've seen before include "Playing live - together" , "Acting together" , "Working together" , "All together - at a musical entertainment?" , "on stage?" .)