I agree with loopy. I have a dangle on my phone and it gets tugged and yanked a LOT so it has to be strong. At least as strong as a bracelet, if not stronger.
Yes, Artistic wire will work harden but since it's got a copper core it doesn't harden as much as pure sterling. I use Artistic wire a lot but I wouldn't use it for a cell phone dangle unless it's 16 or 14 gauge and, like loopy says, in short rather than long elements. And I would use wrapped loops, no jump rings or eye loops, for added strength and durability.