How to load JS for specific screen size using wp_enqueue_script?

At this point I can not think of a way to do what you ask in php (maybe in javascript), but perhaps approaching the problem differently, can serve you detect the mobile device in a better way using mobile-detect[1], wp_is_mobile() as it is very basic, only detects if mobile, but does not distinguish between phones or tablets.

And there is already a plugin for wordpress[2], and this library have a lot examples[3]

  1. https://github.com/serbanghita/Mobile-Detect
  2. http://wordpress.org/plugins/wp-mobile-detect/
  3. https://github.com/serbanghita/Mobile-Detect/wiki/Code-examples