Home Stereo Question - Major First World Problem

I'd like to get some suggestions on my home stereo set-up. I have a stereo system/tv/etc. in my den. I have speakers mounted in the ceiling of the patio, but the wires are only run to the stereo inside.

What would I need to buy to make it so that I can play music from my phone via bluetooth and have it play on the outside speakers?

As it stands now, I have to plug my phone into the stereo inside, so the music from my phone will play on the outside speakers.

I looked at Sonos, but that seems like it does way more than I need. It streams music AND connects to bluetooth. I just need the bluetooth part.

I appreciate any ideas.