JRemote has a feature to play to "this device", which is your phone. If you set up a BT connection to your speaker, JRemote can play to it, because it's connected to "this device".
However, "this device" is special. It is NOT A ZONE. MC can not play to a JRemote "this device" connection. Only JRemote can play to "this device".
There are other ways to do this, but not with JRemote. The only other way I'm fairly certain about, is to use Bubble UPNP on an Android phone. MC can see a Bubble UPNP server on an Android and use it as a zone via DLNA. I'm betting you're using an i-device though. (just a guess)
I've essentially given up on that whole "remote music from MC to phone". Instead I now have a dedicated "phone" device that has a 64 GB SD card in it. I then play from the card using a music player app called Rocket Player. This removes MC from the equation entirely. Except that I (of course) use MC to sync playlists and songs to this phone. So MC is ultimately the source of music for this phone. But it's a true standalone portable, which is how I like it. Simple. No other considerations.
Brian.