Cheers from small Thebes throng (3,3,4)
I believe the answer is:
all the best
'cheers' is the definition.
(I've seen this before)
'from small thebes throng' is the wordplay.
'from' indicates the answer is hidden within the clue.
'ALL THE BEST' is hidden in the letters of 'small thebes throng'.
(Other definitions for all the best that I've seen before include "Pick of the bunch" , "Without exception, unsurpassed" , "A goodwill message" , "A greeting" , "Cheers" .)