Hit it off board (3,2)
I believe the answer is:
get on
This clue is a double definition.
'hit it off' is the first definition.
(I've seen this before)
'board' is the second definition.
(I've seen this before)
(Other definitions for get on that I've seen before include "What boarders do" , "Hit it off" , "fare" , "Board; establish good relations" , "Age; prosper" .)