Question: how to play music on iphone to homepod?
Answer: Open the Music or Podcasts app on your iOS or iPadOS device, then tap the playback controls.
Tap. , then select your HomePod.
To return to the playback screen, tap outside of the AirPlay options.
Tap. ... 
To add an item to the Up Next queue on HomePod, touch and hold the item, then tap Play Next.