New in iOS 13 is the ability to “hand off” music from an iPhone to a HomePod. If you’re playing any audio on your iPhone, just go near your HomePod (or near one HomePod of a stereo pair), and after a few seconds, the audio will switch from the iPhone to the HomePod.
What this essentially does is switch the output from the iPhone via AirPlay to the Home Pod.
As you can see here, the iPhone shows all available AirPlay devices that are active in my home. Music that I was playing on the iPhone (top) then started playing in the bedroom.
As you can see in this interface, you can control a number of AirPlay devices from your iPhone or iPad, sending music to each of them, or controlling playback from Apple Music or your music in the cloud.
What I’d like to see in addition to this is the ability to hand music off from my Mac to my iPhone. If I’m listening to something on my Mac then want to go out, it would be great to pass the music over to that device. It wouldn’t be the same as with the iPhone to the HomePod, which is essentially just playing the music via AirPlay, but it would be more like when you open a web page in Safari, and can then load the same page quickly on an iOS device. Naturally, this would only work with Apple Music or with your music library in the cloud, but it would be a useful addition to the web of Apple devices.