Solution:
One way you could do this is to only initialise fancybox when the screen is larger than mobile.
For example, if you wanted to use fancybox for all devices above iPhone landscape, you would use the following javascript:
$(document).ready(function() {
if ($(window).width() > 480) {
$('.fancybox').fancybox();
}
});
The logic behind the above code is that when the document is ready, we will check whether the window width is larger than 480px which is what iPhone landscape is, if larger than 480px, initialise fancybox.
I hope this helps. Good luck! =)