Artemis is the Goddess of hunting, virginity, and the moon and is the protector of animals. Artemis fiercely preserves her virginity and was followed by virgins, typically why Hippolytus followed her so avidly. There are references to Hippolytus hearing Artemis, as he is a virgin and attributed to having special powers because of this. Artemis has primarily has a symbolic role before the play even begins. Callimachus wrote a hymn to Artemis that tells us that King Minos pursued Artemis and she jumped into the sea, a fisherman then caught her. This is important as Phaedra was Minos's daughter and Artemis dislikes Phaedra. Perhaps this gives just cause for Artemis not to interfere with Phaedras death, only with the outcome of Hippolytus. Aphrodite is the Goddess of erotic love. Even though she is the Goddess of love she does not uphold the values of marriage as she has an affair. This may be why Hippolytus dislikes her as he keeps oaths, as is shown by his keeping his oath to the Nurse.
The tragedy begins with Aphrodite and ends with Artemis. It is possible that Aphrodite spoke her prologue from the stage, as most prologues are human. Artemis appeared as a Goddess from above the action. This is diametrically opposed as to what they represent.
Artemis' intervention is arguably not necessary or probable. This is an instance where the Goddess meets Euripides needs. He has constructed ignorance at a human level and so he can only bring the truth out by divine intervention. The device that makes Artemis' involvement seem natural to the audience is the balance between Aphrodite in the prologue and Artemis in the epilogue.
Artemis is also used for her role in hating Aphrodite, she says "For the Goddess most hated by me and all who love virginity . .goaded her into a passionate desire for your son" this also rids Phaedra of any blame as it was divine intervention that brought about her lust. At least Artemis f...