The horn like form passively (with no additional electronics or power) amplifies the iPhone's internal speaker. 

 

To minimize material used during printing and increase portability the design makes use of the internationally ubiquitous and standardized credit card (or bank card, ID card or similar) to provide support both in the portrait and landscape orientations. Or leave the card out and place the phone flat on it's back for 360 degree bass thumping sound! Ok, that may be a stretch, but it does produce a noticeably louder and fuller sound.