Staccato has one phase either A: because I thought it'd be too complicated for one boss with multiple patterns at that level, or B: because I felt like it. I'm not sure which it was.
Either way, you want to be circling the boss. Slowly. As Ptarth says, short steps are the trick. Note that the more you move at a time, the more distorted the pattern becomes, and the more distorted it is, the harder it is to dodge. There are a variety of other things in the game... including the Warden... that use patterns that are based on distortion, so learning to move slowly and carefully to keep such patterns from going nuts is important.
If you think THAT is hard though, try fighting Staccato on Hard mode. The hard-mode version of that boss is actually getting a nerf with the next update because I went just a BIT overboard.
EDIT: Oh. I just noticed "hard" in the topic title. So you ARE playing that version of this boss. Yyyyyyep. Yep. It's... . it's a thing.
Hmm. The "circle it" tactic doesn't quite work against the Hard version. I might make a quick video a bit later just to show how the fight is supposed to go. Er. Provided that I can. I *really* went too far with that one... it even gives me trouble sometimes.