Proceed to mount (3,2)
I believe the answer is:
get on
I believe this clue is a double definition.
'proceed' is the first definition.
(thesaurus)
'mount' is the second definition.
('get on' can be a synonym of 'mount')
'to' acts as a link.
(Other definitions for get on that I've seen before include "Make progress, do well in life" , "Board vehicle or make progress" , "Board (a bus)" , "Make progress; be friends" , "Hit it off" .)