Hi I had the same problem as you and actually have the same DUT as me.
Here is what I did...
Pair your Linux PC with phone.
Install cu from the repositories.
Open terminal window and type...
You should see something like...
sdptool add --channel=2 SP
rfcomm listen rfcomm2 2
On the phone do Options > BT console > Select the PC you are connecting to
Waiting for connection on channel 2
Then you'll see...
Open a second terminal window and type...
Connection from 00:19:B7:4B:DF:9E to /dev/rfcomm2
Press CTRL-C for hangup
Hit return and when you see >>> type...
appuifw.note(u"This works", "info")