enqueue styles for only mobile wp

If you look at the code of wp_is_mobile you will see that this returns true based on the user agent sent by the browser. It looks for the word ‘mobile’ in the user agent’s name or some other strings that point to mobile devices, like ‘android’ and ‘kindle’. So, that should work.

However, if you are using any caching plugin that plugin will serve the page regardless of the user agent. After all, caching wouldn’t make sense if you would rebuild the page every time a different user agent came in.