Little dog holds a little back to drink (3,2)
I believe the answer is:
lap up
'drink' is the definition.
(lapping up is a kind of drinking)
'little dog holds a little back' is the wordplay.
'little dog' becomes 'pup'.
'holds' is a charade indicator (letters next to each other).
'little' becomes 'l' (this could be a standard abbreviation of which I'm unaware).
'back' says the letters should be written in reverse.
'pup'+'a'+'l'='pupal'
'pupal' reversed gives 'LAP UP'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for lap up that I've seen before include "Assimilate with relish" , "Scoop" , "Relish (with the tongue?)" , "Delight" , "Drink (water) like a dog" .)