If you'd asked me ten years ago whether it would be a good thing to have music playing everywhere I went I'd have answered with a pretty unqualified "yes". And yet, for some reason, people playing music over their phones* in public places are considered a nuisance or possibly even a menace.
I can't believe this is merely because the quality of sound reproduction currently achievable via phone speakers is currently so poor. If the speakers improve - and they will, of course - to the point at which it sounded as good as your hifi at home, people would still protest.
Because - of course - it's not about the music, it's about the territoriality. Like birdsong and the less salubrious habits of dogs, playing music in a public space is just a form of territorial pissing, a cry of "this is my space".
I find that if you just treat it as free music the whole annoyance evaporates. Sure, it's poorly-reproduced music that you might not have chosen ideally for yourself but it's better than the muzak in most shops. Think of it not as a noise intended to signify that "this is my space" but some fool playing you music for free and it all seems oddly pleasanter.
(Update: Peter in comments suggests "they're buskers who don't expect a coin". Exactly what I was trying to say.)
*I think the "mobile" part of this term became redundant about two years ago when I got rid of my landline