neural Siri voice on speak screen not working

Hi friends!
So I heard on one of the forum posts here on Applevis, and also on the podcast Mosen At Large (just got to know that today), that speak screen will use the neural voice when choosing a Siri voice. Well I have the first generation iPhone SE and Siri voice 4 American as my choice, and it doesn't work. I followed everything that Jonathan talked about, and though it worked for his device, it didn't happen on mine. My iPhone was still using the concatenated version of the voice that VoiceOver uses. Am I doing anything wrong? Or is this more device specific?
I wonder if you are using an older device like me, if you had ever gotten it to work on your older iPhones?
Thanks!
David