Quiet Siri, you are talking too much
By default, Siri likes to chat, confirming what you say and speaking the results of your commands when appropriate. If you don’t like all that banter, go to Settings > Siri > Voice Feedback and select either Control with Ring Switch (the iPhone’s physical switch) or Control with Mute Setting (iPad) to make Siri be quiet when the device is muted. Alternatively, choose Hands-Free Only to silence Siri except when connected to Bluetooth, headphones or CarPlay. Or set Siri to whisper—hold the Home button to invoke Siri and then reduce the volume, which applies only to Siri’s voice.
