Muchos kudos to Freewill, webmaster at Bungie Sightings, who scanned in and posted a sidebar from the most recent issue of Next Generation magazine. The sidebar, which focusses mostly on Halo, also has a tantilizing bit of information from this quote:
What is even more impressive is Fantasy Siege -- a totally different game running on the same engine. The engine is a very important thing to us and is a huge part of the deal.
An insight into Phoenix? If so, let's hope Fantasy Siege is just a development moniker. ;)