I stream music from anywhere to my Echo's Bluetooth using my iPhone, iPad and Kindle tablet. When I say "from anywhere" I am referring to music stored on drives that are part of my home network, my cloud, or from music apps (e.g. Slacker, TuneIn, etc). In fact, I hardly have any media (i.e. music, video, photos) stored on my mobile devices -- I do not have to since I can stream the media right from the source to my mobile devices and onward with Bluetooth.
About the only tip I can think of to pass on to you is to be sure your phone and Echo's Bluetooth are connected to one another. Alexa will tell you that the Bluetooth is connected when they hook up.