I'm calling shenanigans.
1) I'm not sure you can host meterpreter on a webpage (which is what you'd need).
2) Even if you did, you don't get shell on an iPhone.
3) And it won't run unsigned apps.
And I tried it, and my iPhone came up with all sorts of mispronunciations. So It would be pretty hard to get t to go to the correct page, ANYWAY.
Plus, a lot of people turn Siri off from the lock screen and/or turn off 'Hey Siri', completely blocking this.
Although using ultrasonics to just get siri to do stuff and so freaking out people sounds cool.