Last July, Waze finally integrated with Android Auto, but the service was limited. Android Auto has two parts: What you can see on the car's display unit and what is available on your phone's screen. Previously Waze was only available through the car's screen, but Android Police noticed you can now access it as an option on phones as well.
The Waze app has long been available for Android phones. This new update, however, is specifically referring to Waze on Android Auto on phones. This means you don't need a car display unit to be able to use Waze on Android Auto.
This news comes on the heels of Apple's announcement that iOS will finally open CarPlay to third-party maps with iOS 12. Waze and Google Maps will likely both be available when the new OS version launches this fall.