Iphone Siri outside of local wifi

Hello. I would like to ask for some advice. I have subscribed to Nabucasa to access my Home Assistant outside my local Wi-Fi. In HA, I have the Homekit bridge integration, and on my iPhone, I have the Home app where I can see and control all my devices. The problem occurs when I am outside my local Wi-Fi network. On the iPhone Home app, all my devices are unavailable, and I cannot control them using Siri either.

Is it necessary to buy an Apple HomePod, or should it work without one?