Field of activity (6)
'field of activity' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sphere that I've seen before include "Field; globe" , "Globe or domain" , "Solid figure - range of activity" , "Ball or field of influence" , "Globe or ball" .)
(Other definitions for purview that I've seen before include "... experience range" , "Range (of experience/thought)" , "Scope of concern" , "Ken" , "Range of thought" .)