I can't say exactly what the problem is, but the 3.5mm socket connections on phones is not standardised and not necessarily compatible with stereo headphones, as an extra connection is required for the mic, which also often has to double as a connection for a button to pick up or put down a call. There's a good discussion of this which may help you understand what's going on with information about the various standards on Wkipedia - https://en.wikipedia.org/wiki/Phone_connector_(audio)#Mobile_phones