Publish online document viewing as a 'fit to screen' on iPhone?

Hi there.

I'm creating a document in InDesign with interactivity (MOS, buttons etc) that I want to publish online and view on mobile. In Indesign, I'm using the doc ument width of 1125 px as per the template for iPhone X when I create a new document. I want this to fill the width of the iPhone screen, and make the heigh/length of the doc longer so I can scroll down and view the rest of the document. To be honest I'm not 100% sure I can actually do this with punblish online...I used to be able to do it with DPS on he ipad about 10 years ago. 

The problem is when I view the published document on my iphone it's filling the length of the doc to fit the height of my screen, much like a when viewing a PDF and its set to 'fit page'

Is there a way round this and is it even possible to fit the width of the published doc to my iphone screen width? ie to view at 100% and then be able to scroll down to access the rest of the content? (much like when laying out  an email at 600px width for desktop?)

Thanks in advance for any help...

Steve