The iPhone app "Clock Wave" is able to generate and transmit this signal from the speaker (!) in your iPhone, so you can accurately set radio-controlled clocks and watches if you cannot receive the real thing. It can simulate the five major time transmitters around the world.
The app has the phone's audio output circuit send a modulated 20KHz tone to the headphones or speaker. This incidentally results in faint EM emission at the third harmonic (60KHz) which can be detected by the watch at short range.
Is it actually receiving WWVB, et al., or jusy synchronizing with, for example, an NTP server and then using that to generate an audio signal you can "manually" sync with?
I don't think the iPhone nor any Android phone have the necessary circuitry to receive the WWVB signal directly. THey do, however, keep time sync with NTP or some NTP-like service over the wireless network or wifi. That should keep it's knowledge of time accurate to a second or two.
I'm always amazed that it works at all.