I did that for a while.  Then I got an HTC One with front speakers.  

Decided to pick up a [Jam Plus](http://www.hmdxaudio.com/portable-speakers/jam-plus-wireless-bluetooth-speaker.html).  A single one is loud as fuck, we keep it to about half volume.  Another cook bought one as well, when you link them together, you can make it stereo.  Also, it reaches wirelessly back to the prep area and the line at the same time.

The best part is, there's no speakers to drive by the phone itself, just data over bluetooth.  Your battery life will go 10+ hours without a recharge on your phone, plus, it's safe in your pocket or otherwise out of the line of fire while working.  The speaker itself goes for about 12 hours.

As far as I'm personally concerned, it was $60 well spent.

Quick Edit:  Switching phone to phone is a pain until you learn the little 'trick' of that thing.    Everyone can have a go at the music, then.