Intercom in Homepod

As noted at the top of the article:

Intercom lets you send and receive messages from one HomePod or HomePod mini to another, or with iPhone, iPad, iPod touch, Apple Watch and CarPlay.

In the context of Apple's Home ecosystem iOS devices are not devices in the Home that can be the target for commands.

tt2

You should be able to intercom from your iPhone to HomePod, you may then be able to reply, but I don't think you can start a conversation from HomePod to an iPhone. See Use HomePod as an intercom - Apple Support for details.

tt2