Take a look at the Settings app.
Go to Siri & Search - Ask Siri -Voice Feedback. If you chose „Hands-Free Only“, Siri will talk when you use „Hey Siri“, or when you‘re connected to a Bluetooth device. If „Control with Ring Switch“ is enabled, Siri won‘t talk when you mute your iPhone (with the button next to Volume).
Siri will provide voice feedback, if you select „Always On“. In that case, Siri will also talk to you when you‘ve set your device to silent.
Hope that helps.