While I'm not a Physics student (I do biology) I'm very familliar with the French system. In France (and most Europe) you can't do a PhD without doing what they call Master Recherche.
In France they are basically 2 kind of Master, Master Recherche (for doing a phd later) or Master Professionel (which is supposed to prepare you to work without doing a PhD)
In the states what is called a PhD is a 5 year program (or often more) that includes the Master (2 years) and then the PhD part of it (the thesis dissertation)
In France you do first a Master (2 years) and then you apply for research PhD (3 years or more).
Also the ENS is focused on research, I would be very surprised if they have a Master Professionelle (I really can't say for physics, but I know that in Biology the ENS Lyon master is a master recherche for research), so if you go for the Master in France you would be expected to go afterward for a 3/4 year phd.