Christian Moral Theology and Philosophical Ethics may seem to be talking about the same subject, that is to learn and understand human behavior and knowing what is right and wrong. However, the main difference there is about Christian Moral Theology and Philosophical Ethics is that Moral Theology focuses more on morality with the faith of people. While Philosophical Ethics focuses on the reasoning of people in knowing what is right and wrong.
Christian Moral theology studies the behavior of humans under the guidance of God. The faith in God and other Christian beliefs are important in Moral Theology since it is believed that knowing what is right and wrong could only be done by holding on the faith that is given to the people by the Father Almighty. According to question 357 in Compendium of the Cathecism of the Catholic Church, the faith of the people is strengthened as they receive the sacraments because they also get the "grace of Christ and gifts of the Holy Spirit". Moral Theology, thus, speaks to the Church.
Philosophical Ethics on the other hand studies human behavior in a way that he is able to reach his natural end. It uses natural reason alone, without the help of faith and Christian beliefs, in order to find out and learn what is right and wrong. Philosophical Ethics uses only intellect and reasoning in order to learn about human behavior. While Moral Theology speaks primarily to the church, Philosophical Ethics talks to a larger group in the society such as universities, corporations, etc.