Of course we pre-suppose good quality music files and good IEMs, or CIEMs, etc.
A mobile phone might have interference etc but a decent DAP should be more than acceptable? For example, would the extra DAC and extra amp in the Fiio X5ii really be discernible over a X3ii when Mojo-ed?
I don't have a Mojo and I don't use my phone to play music. I have tried it just to see how it sounds, its okay, nothing great. I have a Galaxy S4. Then we have the flip side, I heard the K10 earlier this year at a show out of someones phone. He uses Tidal or one of the streaming services, it sounded amazing with the song he had me listen to. Not sure which phone he had though.