Breakpoint 320px don't display in iPhone

I have a hype document in Desktop layout, iPad landscape, iPad portrait and iPhone 320px breakpoint but it seems I'm doing something wrong, when I try to see in my iPhone don't display it the correct version.
Viewport width is in Document Width or maybe I have to select Device Width on mobile options?

I would appreciate any help, please. Is a very important presentation file, here is a link to see: Troconi-Letayf and Campbell presentation
Thank you so much.

yes, if it's not embeded try width=device-width


Thank you so much for your solution! All is working fine now...