Which iPhone does HomePod mini use to make telephone calls?

When making a telephone call using a HomePod mini, does anyone know what iPhone is used to make the call? Is it limited to the iPhone associated with the Apple ID used to set up the HomePod mini, or can it access and use any iPhone on the local Wi-Fi network?

Reading through the Apple Support page, it seems clear that for emergency calls, the Wi-Fi network will be searched for any available iPhone, but it does not say that it works the in same way for ordinary calls. Thank you for any information you can provide.