Best to return bonus put in pocket (3,6)
I believe the answer is:
top drawer
'best' is the definition.
(informal phrase meaning the best available)
'return bonus put in pocket' is the wordplay.
'return' shows that the letters should be reversed in order.
'bonus' becomes 'reward'.
'put in pocket' becomes 'pot' (as in potting a ball in a pocket in snooker).
'reward'+'pot'='rewardpot'
'rewardpot' backwards is 'TOP-DRAWER'.
'to' is the link.
(Other definitions for top drawer that I've seen before include "Highest social position - or sliding furniture box" , "Highest level of society" , "upper class" , "such as da Vinci?" , "highest quality" .)