Don't have an iPhone but just checked on a Galaxy S8 using the Samsung Internet browser and I can pinch zoom the contents of the html and web popups. The Image 1 & Image 2 popups have no zoom and instead the pano in the background zooms.
Hope that helps.
Yeah that's the expected behaviour. I'm tryiong to implement the image zoom, by cheating and sticking the images into an HTML div. It works great on New(ish) android devices as you see, but apparently some people seem to be having trouble on ios to pinzh zoom the html popups. Just tryiung to get to the bottom of it as even in this thread, some people can with ios and some can't with ios. Just trying to understand whats broken where.
From Klous' example I would have thought it should work everywhere, but some people are having trouble with ios.....