Unless your TV allows the optical output to be active while the TV speakers are on your only option will be to split the optical output and connect a soundbar to one of the outputs and the Phonak transmitter to the other one.
On some Samsung TVs there is a quickset menu that will allow you to turn the TV speakers on while the optical output is active even though you can't set it that way in the audio menu itself.
I have always been annoyed that TV manufacturers limit the way TV audio works. I there is no reason they have to turn the TV speakers off. They just decide that you don't need both active at the same time.