Thanks, none of those are the same issue.
I have got round it by manually creating the Exchange settings on the iphone.
The problem is easily replicated on any platform with any browser. I also tried it from a different network (the server resides in our DMZ) It's not just happening to the iPhone x.
Open https:// <url of our serverl>/servlet/traveler
This displays correctly and we can log in. Once we select any links it generates a 404, with the exception of the link back to the apple store.
This has previoulsy worked flawlessly and I haven't made any changes so still confused....