Didn't see anything myself but my mate in Rotherham was actually showing me some footage on his phone last week that looked similar - not Phoenix obviously but same sort of triangular formation, three lights holding position then just sort of drifting apart slowly. He had no idea what it was.
Was it a completely silent thing or did you hear any sound at all? That seems to be the big question with these triangle sightings, the silent ones are the ones that really get me. Planes and helicopters you can always hear something but people keep reporting these things making absolutely no noise whatsoever.
Also how long did it hang around for before it disappeared? Did it shoot off fast or just gradually fade out?