It depends on the GNSS chipset in the phone, but usually it'll be all the GNSS satellites visible in the sky, from all major constellations. The current Android platform supports GPS, SBAS, GLONASS, QZSS, BEIDOU, GALILEO, and IRNSS[0].

Each satellite adds another constraint, which helps, and with more satellites to choose from, you can drop the weakest or worst measurements.

[0] https://developer.android.com/reference/android/location/Gns...()