Siri says I need to unlock my iPhone first

I don’t know how long you have been using an iPhone but I agree with the OP. I used to be able to send messages while driving with Siri while my phone is locked. But not anymore. I have made adjustments so Siri will read me received messages but I can’t reply while driving. Which is ridiculous.

And you are wrong. I can’t use “hey siri” to activate it on anyone else’s phones nearby. When I am with others that also have iPhones and I say “hey siri”, only MY Siri responds. Heck, even with my iPad right next to my iPhone, Siri defaults to my phone and my iPad Siri instantly goes quiet.

So I don’t understand why you are suggesting otherwise.

To run most apps on your phone you need to unlock it. That is a basic security feature; it’s there so someone doesn’t just pick up your phone and run apps. Thus, to run any app that might contain personal data, such as email, messages, notes, etc, the phone must be unlocked. You can ask Siri for the weather, because weather data are not personal. But you can’t ask Siri to read your messages, or show your photos, unless it is unlocked, because if you could ANYONE could; just pick up your phone and say, "Hey Siri, read my messages”, or “Hey Siri, transfer $10,000 from my Apple Cash to John Doe"

Siri does not have speaker recognition; it can’t distinguish you from anyone else speaking, except for "Hey Siri". And you don’t train it to recognize you; training is to recognize your accents. And you can also invoke Siri by holding the side button, and that will work for any speaker. Speaker recognition would require hours of training, not 2 minutes.

I don’t see what facial recognition has to do with Siri; FaceID cannot be fooled; it recognizes you, and only you.