Pretty sure the echo by default will stream music from Amazon music, it doesn't take anything from any connected device. So for this you will need to be logged into an account with a Prime subscription.
Otherwise, you can add other sources like spotify, deezer or apple music which it can stream the music from.
Edit: rereading it, sounds like you can connect your phone via bluetooth to play music from the device, but can't say I can comment on how it's used. Not sure if it works with voice.