Not altogether playing a role (2,4)
I believe the answer is:
in part
'not altogether' is the definition.
('in part' is the opposite to 'altogether')
'playing a role' is the wordplay.
'playing' becomes 'in'.
'a role' becomes 'part' ('part' can be a synonym of 'role').
'in'+'part'='IN PART'
(Other definitions for in part that I've seen before include "To some extent (though not entirely)" , "to some degree" , "Not fully engaged" , "No longer resting as actor" .)