I’ve found a better way than from my post just above:
In VST Connections. Activate Control Room Channel (it probably already is). Main is set to device ports Mix 1 L and Mix 1 R (which I think is the default). In Hardware Set Up, Phones1 is controlled by the “Main Control Room Channel.” You can listen to the Mix or any cue send you’ve set up in the Main section by clicking on the appropriate button (Mix…C1…C2…).
For Phones2: Activate Phones Channel in Control Room Mixer. In VST Connections, the Phones channel should be connected and set to Mix 2 L and Mix 2 R. By clicking on Mix 1 L/R in Hardware Set Up/Phones2, the listener will hear the Main Control Room Channel (Mix…C1…C2…); by selecting Mix 2 L/R in Phones2, the listener will hear the Phones Channel (Mix…C1…C2…).
I hope this is clearer!