You will have to check the manual for the Bose receiver. If it has a bluetooth receiver (which I suspect it does) then it is designed to stream from the phone to it.
That is the opposite of what you want. You want it to have a bluetooth transmitter that can send audio to the speaker.
You could make it work by adding a bluetooth transmitter to it. How you would connect that depends on the receiver. You could use preout or use a speaker to line level converter. A car or marine stereo guy could set you up.