phanna dashdance is using the foxtrot (opening animation of dash) to have an extended distance dashdance. It's pretty useless for Sheik because her opening dash animation is so short to begin with. In fact, it's part of what makes her shield dash so great.
Also, ****, Tristan. I got hit by like 5 boost usmashes against my friend's Sheik and I still don't feel it's worth learning. It's not amazing, and it's not necessary. My entire plan in fighting games has been to find someone with an easy to pick up moveset so I wouldn't have to wrap my mind around technique and could instead concentrate on more useful things, like smart play.