I believe WhiteHat explains it here at this thread.
I can tell you that my Phonak Lumity Life aids all (4 pairs!) and older Phonak Marvels have “Accoustic Phone” in the dedicated programs lineup.
Other info sites describe Duophone as working exactly like my Accoustic Phone, hence the confusion. Main thing is: we have a need for some program (call it what you will!) that does not rely on BT to stream audio on a phone to both ears stereophonically. 
What I don’t know is whether Oticon aids have such a feature.