The article says the magnetic field is detected by a bracelet which in turn communicates via Bluetooth to the phone.

...which begs the question, why not just control the phone via the bracelet directly if the user needs some kind of remote control facility?

It's a concept, which means that the magnetic field explanation is very much akin to the flimsy pretexts used by science fiction shows to provide some plausible sort of excuse for how something like this might perhaps work maybe.

Concepts are basically what happens when a person who can draw goes "dude, wouldn't it be awesome if X?".