What data do smartphone applications use to predict visible Starlink passes?

Answer

Publicly available orbital data.

Dedicated tracking tools utilize publicly available orbital data to computationally predict the time and location of future visible passes for observers based on their geographical location.

What data do smartphone applications use to predict visible Starlink passes?

#Videos

Starlink satellites, the string of lights in the night sky. - YouTube

What was the string of lights in the sky over the Youngstown area ...

lightobservationskysatellitephenomenon