Honestly done, or not so honestly done (2,3,3)
I believe the answer is:
on the sly
'not so honestly done' is the definition.
'honestly done' is the wordplay.
'done' is an anagram indicator.
'honestly' anagrammed gives 'ON THE SLY'.
'or' is the link.
(Other definitions for on the sly that I've seen before include "Done in an unpleasant and secret way" , "With craft" , "Secretly or furtively" , "in private" , "Under the table" .)