Hmm, I'm not too knowledgeable on the their term of regular phase. I remember reading about it somewhere but I forgot all about it. Interestingly enough, the term "regular phase" is also on the earcups on the original T50.
I think they were intended for studio use. There have been extensive mods using the modern Fostex drivers seen in some companies today such as ZMF headphones, MrSpeakers, and some other less well-known ones.
I've briefly owned the MrSpeakers Alpha Dog and ZMF Ori which I believe both use the same drivers but with a lot of modding.
I wasn't a fan of the Alpha Dog. I thought they looked clunky, felt unnecessarily heavy, and sounded boring. I thought a stock T50RP MK3 sounded much more fun to listen to.
The Ori, however, I thought was fairly nice sounding. Warm and strong bass while still remaining articulate. The wood definitely seems like it's well-made. At the asking price of 899 USD though, I don't think it's worth it in terms of sonic performance. It's more like a "variation" in sound to a stock T50RP MK3 IMO.