You need a Masters' degree. If you are studying in a Masters' course in France, check if this training will issue a Masters' grade, or you may end up studying in a course that does not allow you to register in a Doctorate/PhD.

If you don't have a Masters' degree, but can certify experience in research or a 5-years long Bachelor, you can ask your Doctoral School for an exemption to directly join a doctorate/PhD course.