Phantom Dust won't be appearing at the ongoing Gamescom conference, according to comments made by Phil Spencer, head of Microsoft's Xbox division.
Game Informer approached Spencer at Gamescom to ask about Phantom Dust but were met with vague possibilities. After noting that the game won't be appearing at Gamescom, Spencer likewise expressed doubts that Phantom Dust would be shown at this September's Tokyo Game Show. "I would bet [Phantom Dust] won't be [at] TGS," Spencer said. Game Informer speculates that the game will appear at E3 2015 based on "the schedule of events following [Tokyo Game Show]," indicating they don't expect it to surface at the next major industry event after TGS, the 2015 Game Developer's Conference in March.
Whether Phantom Dust is next seen at GDC or E3, it seems unlikely that we'll see any more from the revived cult-classic until next year.