Hello Steve, I did think as Publish Online is a new development, that this feature has not been developed yet. Thought I'd just check incase I'd missed something. I do think Publishing Online is a handy new tool and I have submitted a Features Request as suggested. Many thanks.
If you turn ON the setting for auto-rotation on your phone and rotate your phone from portrait to landscape then you can view the document in landscape format. This setting resides where other phone level settings are present (in most cases, "Settings" application in phone menu).
Sorry for wasting your time - my screen view was locked in on Portrait mode! This must have been done accidentally on my iPhone as I nearly always have it unlocked.
And yes I can view my documents in landscape format now.