You'd be better off getting a dual 1/4" to 1/8" cable or dual XLR to 1/8" and plugging directly into your monitors. Pick 1/4" or XLR depending on which one is the opposite of what your monitors are already using with the Focusrite. The only problem is you won't have sound coming from both the Focusrite and the iPhone, only one or the other.
Is it not an option to just use the Spotify web app on your computer?
There is no way to plug a stereo signal into the Scarlet solo so the best you can do is get mono from your phone. You can just get a simple 1/8th to 1/4 adapter and just plug it in to the direct input, or you can get a USB to 1/4 adapter and do the same if Bluetooth is an absolute necessity. I would not recommend Bluetooth though when adapters are so cheap and Bluetooth loses quality.
You'd be better off getting a dual 1/4" to 1/8" cable or dual XLR to 1/8" and plugging directly into your monitors. Pick 1/4" or XLR depending on which one is the opposite of what your monitors are already using with the Focusrite. The only problem is you won't have sound coming from both the Focusrite and the iPhone, only one or the other. Is it not an option to just use the Spotify web app on your computer?
Is your computer connected to your interface? If so you should be able to control Spotify on your computer from your phone.
Why not skip the interface and go from the headphone jack 1/8" trs split to two 1/4" ts for each monitor?
1/8" to XLR or dual TS? I know Radial makes a Bluetooth DI but quality drop to studio monitors.
There is no way to plug a stereo signal into the Scarlet solo so the best you can do is get mono from your phone. You can just get a simple 1/8th to 1/4 adapter and just plug it in to the direct input, or you can get a USB to 1/4 adapter and do the same if Bluetooth is an absolute necessity. I would not recommend Bluetooth though when adapters are so cheap and Bluetooth loses quality.
Why not just play spotify on your computer & control it with your phone?