Eric,
Phase Technology makes their own drivers. Not a big company at all. Though their parent company, United Speaker Systems, is one of the biggest in the world. However, the drivers made by Phase Tech. (not United Speakers Systems) I believe are only produced for Phase Tech. Speakers (at least their PC line). They hand make everything in Florida. Of course they don't make the wire in which they wind their own voice coils with, or make the resistors, etc. they put in their crossovers (though maybe United Speaker Systems does). But the drivers, you betcha, cabinets too (though it goes without saying they don't "mill" their own wood!

)! For those who don't know (maybe it's been mentioned already), the founder, Bill Hecht invented the soft dome tweeter!
FWIW, As the owner of my local Hi-end Audio store put it:
"Because Mr. Hecht and Phase Tech. has all those royalties coming in with all their patents and supplying other speaker companies with parts, he can afford to custom make Phase Tech. speakers with all their special designs and still offer them at a reasonable price."
They are mostly sold through custom installers, yet are very well priced without mass producing them. Very Cool.... if you ask me!
Best Regards,
Patrick