Genuine question for anyone who was there - did it make any sound at all? I wasn't in Phoenix (I'm in Notts, England) but I've been tracking similar triangle reports for about 15 years and the noise thing is always the detail that separates the interesting cases from the boring ones.
Most military craft, even slow-moving ones, produce some kind of engine noise. The cases that stick with me from my own research are the ones where witnesses describe complete silence or sometimes that low hum that you almost feel more than hear.
What were the weather conditions like? Clear sky, any wind? And did it move in a straight line or was there any course correction? Those two details will tell me more than anything else about what we're actually dealing with here.
Not saying its definitely something unusual, just that triangles over urban areas at that hour are worth documenting properly rather than just chucking on Reddit and forgetting about.