They claim to be able to track FRS ptt radios, which implies a sensitivity to .5w transmissions, and iirc a phone will put out max .2w (on 4g). Lower, yes, but not massively so, so if it really does work on FRS I wouldn't be shocked if it worked on a conventional smartphone. The phone operating in a higher frequency range than ~470mhz frs/gmrs is admittently an additional challenge, but since the thing runs up to 15ghz I wouldn't count on it being unable to track a phone