Ndo,
As I say, the Trophy has 2 bluetooth channels:
1) "Headset 1" - for your main rider bluetooth headset/helmet
2) "Device 2". - for either a pillion headset, phone or bluetooth-enabled mp3 player or satnav
If you have an iPhone you also have the option of connecting it via the USB socket in the left fairing pocket. I understand that the bike will then play music as if it was an iPod.
Which source you are listening to, volume, tone etc, are then selected by the left handlebar control cluster and on-screen menus.
The audio manual supplied with your bike gives you a general idea how to set things up but is pretty vague on the detail.
BP