Board is to make progress (3,2)
I believe the answer is:
get on
I believe this clue is a triple definition!
'board' is the first definition.
(I know that board can be written as get on)
'is to make' is the second definition.
(thesaurus)
'progress' is the third definition.
(synonyms)
(Other definitions for get on that I've seen before include "Make progress; be friends" , "What boarders do" , "Enjoy harmonious relationship" , "Make progress or climb aboard" , "Age; prosper" .)