GPS clocks are not reset. They run at adjusted frequency. In general in a satellite mission you want to avoid resets and be prepared to do adjustments not only for time dilation. In a satellite mission I worked we had an onboard clock that was the source of mission time in "milliseconds" since the satellite was powered on soon before the launch. The clock was never adjusted or reset. Time dilation and other errors accumulated. The satellite periodically transmitted a GPS time stamp along with the mission time to the mission control. Based on that the mission control uploaded a schedule of actions in mission time.

If your phone is not compatible with calls over 4G (does not support your carrier's configuration of VoLTE) or 5G (does not support VoNR) it will switch to 3G or 2G to make a call. Data may not be available or be very limited because not many frequencies are allocated for 3G and 2G these days.