Depends on the DAP. For some (probably most) there is no sonic advantage. The DACs and amps in a decent phone are on par with a decent DAP. That wasn't always the case - a few years ago phones weren't very good for playback. Of course, there are also "audiophile" DAPs like the Astell & Kern that are really in a different class. They are capable of playback of higher bitrate, lossless files and have DACs & amps that are said to be on par with separate audiophile components. Then there's also the sheer storage size. Not all phones will let you get 80 GB or more of music, but again, this has changed more recently and continues to change.