Q: All calendar events on my iphone 5s have moved back one day...what is going on?

Hello cinstaf,

Welcome to the Apple Support Communities!

I understand that events in Calendar are showing one day later than they should while the holiday calendar events remain correct. For this situation, I would first suggest looking at your Time Zone Override settings. The attached article will explain more about this setting and how to adjust it. 

Change Time Zone Override for Calendar on iPhone, iPad and iPod touch - Apple Support

Have a great day