Those material and group name glitches are a big pain in the butt, I agree. You have to hunt down every instance of a group name and make sure it's right in Poser after import. You already know about the problem with illegal characters, like spaces, in material names. What it boils down to is renaming everything in Poser, spawning props, deleting the original obj file, re-assigning material names, then exporting the obj file exactly the way Poser likes it. At that point, the phi file you create is now very likely to work the first time.

That's one of the glitches I've noticed in Carrara. I create a vertex obj and name it something, but it's still called "Vertex Object" in the assembly room. It seems like Carrara also "forgets" material names the same way.