Google's strategy with the Android Auto phone interface has been confusing, to say the least. For a while, you could simply use the Android Auto app to get a head unit-like experience on your phone. That's still basically the current situation, but how we got here is complicated. The most recent update to the phone interface makes Google Maps work better in landscape mode.
A new Google Maps UI is rolling out now for the Android Auto experience. The update to the UI is actually thanks to an update to the Maps app itself and not the Android Auto app. Regardless, the new UI makes Maps work a lot better in landscape mode when used in Auto, which is how a lot of people use their phones when mounted in a car. The changes are present in portrait mode as well, though they're not as noticeable.
The menus and banners that appear at the bottom of the screen now "float." This means they aren't tied to the width of the screen, which becomes important in landscape mode. Rather than stretching the full width and blocking a lot of the Google Maps view, the menus and banners are pushed to the side. You can pull up the menu and still mostly see where you're going. Again, this new UI is rolling out through Google Maps v10.45 (download APK), but it's only visible through Android Auto for Phone Screens. We should expect the Maps UI in the standalone app to adopt this behavior as well.
So what's going on with Android Auto for phones, anyway? A little over a year ago, Google announced the phone app would be dropped in favor of Google Assistant's Driving Mode. A few months later, the company backtracked and said they would be releasing a separate app called "Android Auto for Phone Screens." That app eventually launched, which is where we're at today (though we're still waiting for Google Assistant's Driving Mode).
Both the old Android Auto and new Android Auto for Phone Screens apps are in the Google Play Store and some phones can see both. The reason for that, as explained by XDA's Mishaal Rahman, is the plain "Android Auto" app is now part of Google Mobile Services and so it comes pre-installed on devices running Android 10 or later. The main purpose of the Auto app is for beaming the car interface to your vehicle's head-unit, whether wired or wirelessly. The phone interface has always been secondary to this functionality. The new Android Auto for Phone Screens app is simply a shortcut to the phone interface that exists in the older Auto app. Once Google Assistant Driving Mode rolls out, you'll have to use this shortcut if you want the headunit-like experience on your phone.
Via: Android Police