I'm not sure about that Qantas Club membership. If you sign up for the Platinum Challenge then at the end of that first trip you will have lounge access for all subsequent OW flights, even allowing for the fact that you won't get credit for PHX-LHR. If that first trip is in J then you will have lounge access anyway.

Qantas Club costs AU$625 for one year for Canadian residents. That's very nearly US$500. That seems a ridiculous amount to pay for pre-flight snacks & drinks once in PHX, and access to the (business class) lounges on two transits in LHR. It doesn't get you anything at all if your first trip is in J.