Not exactly. "EX Holon Phantoms" is actually the name of a whole expansion of cards. Like the "Black and White: Emerging Powers" and other things, just a lot more ancient. It depends on what your locality is like, and whether you can buy them easily or not that decide if they are rare.
But on the general count, yes they are pretty rare.
For more detail on these cards, see here.
Hope I helped!