To flatter (6,2)
I believe the answer is:
butter up
'to flatter' is the definition.
(buttering up is a kind of flattering)
This is the entire clue.
(Other definitions for butter up that I've seen before include "Flatter using common dairy product" , "mountain goat?" , "Soft-soap" , "Flatter for a purpose" , "Flatter using dairy product? (6, 2)" .)