I tried the site on three iPhones with iOS 8 and there the site with the gallery is non-responsive, so you see the normal desktop version on the mobile phone.
First of all, please ensure that you are using the most recent version of Juicebox-Lite (v1.4.2) to ensure that any bugs which were present in previous versions but which have since been fixed are not contributing to your problem.
If necessary, you can download the current version of Juicebox-Lite from the download page here.
If your gallery sets screenMode="AUTO" (the default value for this configuration option), then your gallery should be displayed in Small Screen Mode on small screen devices (like the iPhone). (Please see here for more information on how Juicebox adapts to different devices and screen sizes.)
Do you see the problem in both Chrome and Mobile Safari on your iPhones or just in one of these browsers?
Are you able to upload screenshots somewhere of what you are seeing on iOS 7 vs iOS 8 so that I can see what you are seeing? (For example, I do not know if your gallery uses a Splash Page and whether or not this is displayed.)
Also, it may help if I could see the gallery in question so please post the URL to your gallery's web page so that I can investigate further. Thank you.