Send audio output of MacBook to iPhone for remote listening
Yes, using Airfoil for Mac (also available for Windows) and the companion app Airfoil Speakers Touch you can stream any audio from your Mac to your iOS device. 

I haven't tried it much myself, and reviews are mixed, but you can try it for free before shelling out the money for it.

This can also be used to send audio from a MacBook to a bluetooth headset connected to an iOS device. Something which is very difficult otherwise.