Intelligent swimmer working on DPhil (7)
I believe the answer is:
dolphin
'intelligent swimmer' is the definition.
(I've seen this in another clue)
'working on dphil' is the wordplay.
'working' indicates anagramming the letters.
'on'+'dphil'='ondphil'
'ondphil' with letters rearranged gives 'DOLPHIN'.
(Other definitions for dolphin that I've seen before include "Sociable sea mammal, sacred in ancient Greece" , "Small sociable whale" , "Small toothed whale, larger than a porpoise" , "Porpoise-like fish" , "member in school" .)