How to track phone while offline

[Cheeryshio]

... not sure, there is the app called tile, though it still need to be somewhat connected, since the GPS need a connection, though it does locate the last known location of the device if it was connected at that time, which can come in handy

[PaymanHamdard]

I guess thru offline location sharing by network signals.

[RedDogRabbit]

Settings > Biometrics & Security > Find my Mobile Click on it to enable Offline Find my Mobile.

Have a look at the link & Screen Shot. 

Settings > Biometrics & Security > Find my Mobile Click on it to enable Offline Find my Mobile. 

https://www.xda-developers.com/samsung-find-my-mobile-app-locate-galaxy-devices-offline/amp/