It would probably be more accurate to install a stratum 1 NTP server on your phone since it has GPS. But then you'd probably get hit with jitter from Wi-Fi/Bluetooth/USB.
You need to get the PPS to some other device, then it could be done. The whole GPS stratum 1 thing is mostly just PPS. You get the correct time with ntp, and the start of a second with the PPS from the GPS.
