Try leaving Siri out of this.
Force restart iPhone - Apple SupportApple SupportOfficial Apple Support › guide › iphone › ios
Follow the instructions very carefully. You have to keep holding the Side button for 20-30 seconds and ignore the Power Off slider if it appears and wait for the Apple logo to appear in the center of the screen
If still no luck after a few tries, there is a hardware problem with the iPhone that will require service at the Apple Store / Genius Bar or an authorized Apple service shop.
You can find a list of authorized service shops in your area using this link:
Find Locations