iPhone safari https prompts

My company has two https web pages with anonymous access (open to the world).

We recently set up enforced redirection from http to https for thes pages.

Safari on iPhone prompts for credentials, which is not applicable for the pages in question. Pop-up blocker is off.

All other browsers and platforms seem to work with these changes. iPads have no difficulty.

I have not found any iPhone that does not have the issue.

I loaded iFox Free browser on my 4s and it does not deliver the page at all; no prompt, either.

I suspect this might be related to there being no phone version of the pages.

Still, e.g. Windows phones just get on with displaying the standard page layout.

Thank you for any suggestions.

Nick