Envisage accompanying chum to fantastic cinema (7,6)
I believe the answer is:
picture palace
'cinema' is the definition.
('picture palace' can be a synonym of 'cinema')
'envisage accompanying chum to fantastic' is the wordplay.
'envisage' becomes 'picture' (picturing is a kind of envisaging**).
'accompanying' says to put letters next to each other.
'chum' becomes 'pal' ('pal' can be a synonym of 'chum').
'to fantastic' becomes 'ace'.
'picture'+'pal'+'ace'='PICTURE PALACE'
(Other definitions for picture palace that I've seen before include "The Louvre" , "cinema?" .)