Greek character in theatrical Phaedra (5)
I believe the answer is:
alpha
'greek character' is the definition.
(letter from the Greek alphabet)
'in theatrical phaedra' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ALPHA' is hidden in the letters of 'theatrical phaedra'.
(Other definitions for alpha that I've seen before include "high mark" , "piece of Greek writing" , "Beginning" , "Early testing stage for new software or hardware" , "Leading Greek character" .)