The developers often release the stable versions of new phases on the Play Store under the title or simply "Proton Bus Simulator."

To ensure you have the latest features and official map support, you should download the game from the developers' verified channels.

Download steps (typical)

If you use the Steam version, the "Phase 3" transition is handled automatically via the "Beta" branches or standard updates, depending on the current development cycle. What’s New in Phase 3.1? If you are looking for an article to explain