Move forward with father's boy (4,2)
I believe the answer is:
pass on
'move forward' is the definition.
(thesaurus)
'with father's boy' is the wordplay.
'with' means one lot of letters go next to another.
'father's' becomes 'pas' (pa is a kind of father).
'boy' becomes 'son' ('son' can be a synonym of 'boy').
'pas' next to 'son' is 'PASS ON'.
(Other definitions for pass on that I've seen before include "Bequeath" , "Refuse" , "go forward" , "Hand over - die" .)