I'm quite doubtful that a stepper motor will produce a significant amount of power let alone be the best thing to use, I'd be curious to see your source for that claim. Furthermore, with a small propeller and anything short of a gale, I wouldn't be all that surprised if the mechanical "stickiness/clickiness" or the stepper just locked the whole thing up.
Making a regulator seems like a tricky proposition to me, because you need to provide 5V to the phone, while simultaneously drawing the correct amount of current from the generator (if you draw too little current, you're just not getting much power out of the wind; if you draw too much current, you'll just burn up your electricity as heat in the windings. There's an ideal amount of current to draw, which depends on the instantaneous wind speed). Solar panels have a similar issue, and use a technique called MPPT to continuously figure out what the best current to draw is.
That's not a trivial undertaking.
In short, I'm sure there's a clever technique out there that is nice and simple and works "well enough"; evidently I don't know of that technique.