Board agree to progress (3,2)
I believe the answer is:
get on
This clue is a triple definition!
'board' is the first definition.
(I know that board can be written as get on)
'agree' is the second definition.
(I've seen this before)
'to' acts as a link.
'progress' is the third definition.
(synonyms)
(Other definitions for get on that I've seen before include "Agree - embark - make progress" , "Age; prosper" , "Board; establish good relations" , "Make progress; be friends" , "Make progress or mount up" .)