You can’t really change the Hey Siri functionality on iPhone or least I don’t think you can. If I can do that with third-party apps, that would be awesome.
Siri is pretty much worthless at this point. I remember one time I didn’t have a cellular signal so I was thinking oh let’s see what “on device” things that she can do. I asked her what was 2+2. I mean, that’s really simple right? “To do that you’ll need to be online”. To be fair I only have the 14 Pro Max so maybe if I had the new iPhone 16 Pro Max with a more powerful processor it could do addition on device.
If I have a question to be answered by AI, I will use Grok. It’s not as convenient since I have to open up an app versus holding the side button, but the answer will be sort of intelligent.
What I use it for is to go over some ideas and get it input. For example I asked how hard it would it be to convert a Japanese mini truck to electric. If you do this, be sure to double check because AI can have flawed logic and it will give you a flawed answer sometimes.