For your missing icons, it’s “Cross-Origin Request Blocked” issue (CORS).
In firefox browser firebug console, I can see that the font-awesome icon library is prevented from loading.
Please see screenshot. http://prntscr.com/7uqwcx
This the error notice.
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://www.kuhlma-it.de/wp-content/themes/evolve-plus/library/media/js/fontawesome/fonts/fontawesome-webfont.woff2?v=4.3.0. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing).
Your probably has to set header “Access-Control-Allow-Origin” in your .htaccess file.
Please see this article for more details, http://benjaminhorn.io/code/setting-cors-cross-origin-resource-sharing-on-apache-with-correct-response-headers-allowing-everything-through/
I am not familiar with .htaccess file customization and therefore cannot provide a solution for this issue.
As for your iPhone error. Sorry, I am not seeing any, it works properly for me.
Please see screenshot. http://prntscr.com/7uqzpz