I’m surprised if Phonak doesn’t have a setting somewhere for this. With the ReSound Smart 3D app, the TV Streamer appears as a separate program and within the program there are separate app controls for streaming volume and for external mics (effectively heard TV or sound bar volume). And I can control the volume of each ear, both for streaming and external sound, separately. If there is not such an option somewhere in the app, why not send feedback to Phonak requesting such an option, mentioning that other brands of HA’s have it?!
Edit_Update: @StevenC56. While watching Dr. Cliff’s video on the Roger On device, I noticed that he showed how to change the balance between external sound and the Roger On at the following point in his video: https://youtu.be/PHBin5VdKXo?t=605. Have you looked for a similar option when in the TV Connector program choice? Sorry if this suggestion is ignorant (what to expect from a ReSound user!). Oops! Had to update the time in the video link.