can anyone compare "medea" and "phaedra" as a revenge tragedy?
I would imagine that you are referring to Euripides' Medea and Euripides' Hippolytus, the latter play being one in which the character Phaedra appears. The younger Seneca, however, does have plays entitled Medea and Phaedra, respectively.
Whatever the case, both Medea and Phaedra do exact some sort of vengeance upon male characters in their respective plays and in both cases the vengeance could be ascribed to being rejected by these men.
Medea was married to Jason, who divorces her to marry the daughter of Creon, king of Corinth. In retaliation, Medea poisons the princess' clothing, which not only causes her death, but also Creon's death. Medea also kills her children by Jason before she flees Corinth and leaves Jason to live out the rest of his now-miserable life.
As for Phaedra, she was married to Theseus, but she was in love with her stepson, Hippolytus. This young man, however, was devoted to chastity and therefore rejected Phaedra's sexual advances. In an effort to maintain her honor, Phaedra wrote a note accusing Hippolytus of having sexually assaulted her. Then, Phaedra hanged herself. When Theseus read Phaedra's letter, he cursed Hippolytus, which eventually led to Hippolytus being dragged to death by his own horses in a chariot accident.
Thus, both Medea and Phaedra take some sort of vengeance upon men who reject them.