skipper

One correction. You can't set up the HomePod with ANY iPhone. You must be using an iPhone or iPad that uses the same AppleID as the Home in HomeKit.

This is a major gotcha

Imagine that a wife buys a HomePod for her kitchen but her husband has setup HomeKit with his AppleID. She won't be able to use her Notes, Reminders or Calendar through HomePod because HomeKit requires her husband's AppleID to add a device and then HomePod uses that AppleID as the HomePod owner. HomeKit 'steals' her device during setup and gives it to her husband in the setup process even though HomePod may be using her AppleID for music and podcasts.

Perhaps a simple solution would be for HomePod setup to ask who in Family Sharing is the owner of the HomePod and then use that AppleID for Notes, Reminders and Calendars.

Could this problem be caused by the fact that HomePod is both a smart speaker and a HomeKit hub?