If you have some form of an outdoor radio with an Aux port, this is what I do. I bought a bluetooth transmitter (not one for the car) that connects to home sound systems via the audio (red and white) Aux cables. I use SiriusXM through Dish to listen to music. But, I have about 1,100 songs on my Samsung Galaxy through an SD card. That's what I use when I'm outside by my pool. I put my phone on the kitchen table and the bluetooth works right through the window.
The transmitter works off a standard Android charging cable. I just plug it in and charge it, and it works. You can also plug it into an outdoor outlet and leave it on. It will still work. That's what I suggest.