It looks like you might have some custom CSS on your web page (possibly introduced by your theme) which is conflicting with the gallery's own CSS.
You might like to temporarily try using a different theme (such as one of the default WordPress themes, e.g. TwentyTwelve, TwentyThirteen or TwentyFourteen), just to see if this makes a difference.

Also, I notice that your gallery currently sets expandInNewPage="FALSE". Try setting expandInNewPage="TRUE" instead. When the gallery is expanded from the Splash Page, it will be expanded on a new page of its own (instead of being expanded on top of the embedding page) where CSS conflicts cannot occur.

I hope this helps.

The default value for expandInNewPage is AUTO and on iOS devices, this equates to TRUE. Please see here for details.
It should be pretty safe to just keep expandInNewPage="AUTO" (or, indeed, to set expandInNewPage="TRUE") and both settings should certainly work fine.

If your friends were viewing your gallery over a 3G or 4G connection (rather than wi-fi), then please see this FAQ which has a solution to this problem.
Why can't I view my gallery on a 3G mobile connection?

If this does not help, then please let me know what your friends saw instead of your gallery (an error message or a blank space?) so that I can investigate further.

Also, as your WordPress site is on www.kleibography.com (and all paths within your WordPress pages use the 'www' subdomain), please make sure that your friends are visiting www.kleibography.com rather than just kleibography.com. (All gallery files must be on the same domain or subdomain as the web page containing the gallery's embedding code due to the JavaScript same-origin policy.) I doubt that this is the root of your problem as kleibography.com redirects to www.kleibography.com but it might be something worth checking.

A 4G connection may use content modification just like a 3G connection.
Please implement the solution in the FAQ: Why can't I view my gallery on a 3G mobile connection?
In the meantime, please ask your friend to try viewing your gallery over a wi-fi connection and it should hopefully display and function fine.

Maybe with a little more information, we can track this problem down.

Have you tried setting expandInNewPage="TRUE" since implementing the solution for 3G/43G?

What happens when you expand the gallery with expandInNewPage="TRUE" on your own phone? (Does the weird scaling issue occur the first time you expand the gallery or does this happen only when expandInNewPage="FALSE"?)

What phone (and operating system version) do you use?

Have you tried different browsers (e.g. Chrome, stock Android Browser, Mobile Safari)?

On an iOS device, when expandInNewPage="AUTO", the value "TRUE" is used (as noted here) and we know that your friend can expand the gallery successfully in this case. Allowing Juicebox to always expand the gallery in a new page (by setting expandInNewPage="TRUE") should work for all devices and browsers.