In my experience, if you want to use smart home stuff you really need a hub of some sort rather than connecting everything directly to your phone.

Smarthings is popular, or Hubitat for the more tech-savvy. Or just an old PC with HomeAssistant or OpenHAB installed. All have ways to expose their connected devices to HomeKit/Siri.

If you go the old PC route, just make sure not to buy any ZigBee or zWave devices since they’d need additional antenna dongles (built in to the standalone hubs) to function.