Apparently there are a lot of different versions of the Alexa app and not all of them are updated at the same time.
Just off the top of my head, there are differences between the Alexa app on iPhone, iPad, Android, Fire tablet, web app. I'm not sure if there are differences on Android between a tablet and a smartphone. If I had to guess, I'd say there are differences. As a former Android developer, I've always hated making different versions for smartphones and tablets.
Even if a new feature is already enabled on your Echo device, it does not necessarily mean that the Alexa app you are using has been updated to use that new feature.