Encourage dog to come back, employing "heel" essentially (3,2)
I believe the answer is:
gee up
'encourage' is the definition.
(I've seen this before)
'dog to come back employing heel essentially' is the wordplay.
'dog' becomes 'pug' (pug is a kind of dog).
'to come back' shows that the letters should be reversed in order.
'employing' is an insertion indicator.
'essentially' means to look at the middle letters.
The middle of 'heel' is 'ee'.
'pug' reversed gives 'gup'.
'gup' enclosing 'ee' is 'GEE UP'.
(Other definitions for gee up that I've seen before include "Hurry along, Dobbin!" , "Words of encouragement to a horse" , "Hurry up, horse!" , "Command to horse to go faster" , "Go faster, horsey!" .)