Subsidizing is only truly effective when you do it early gen. It takes alot of extra accessory, subscription, and software sales to recoup what you lose when you subsidize a console. Phil was not head of Xbox early this gen when XB1 released, Don Mattrick was. Mattrick made the decision not to subsidize XB1 on launch, not Phil. By the time Phil was head and XB1 X was getting ready to release, it was too late for subsidizing it to have any significant effect, all it would have done is lose them money on hardware sales in exchange for a small increase in userbase. Phil decided that this gen was basically already a lost cause, and that it would be better to focus on profitability over userbase size for the remainder of the generation.
This does not however mean that Phil will do the same thing with Scarlett that he did with X. A new gen is a chance for a fresh start for Xbox, and since subsidizing is most effective when done at the beginning of a gen, he may very will choose to take the fight to Sony by subsidizing a more powerful system to aim for price parity with PS5.
Now do I think that we will see a 50% more powerful console? Not a chance. Maybe 20% more powerful for the same price as PS5 would be my expectation if that is Phil's plan.
Phil took over in 2014. At that point, he could have convinced MS to subsidize the XBO to $299. The X also released in 2017. That was all his baby. He definitely could have had MS subsidize it. The problem? MS, not Phil Spencer, makes that call. And they are not in the game of subsidizing their HW significantly. They have made that obvious. Hell, after the XBO's lackluster results, there was talk of spinning off that division to let it suffer its own fate. Even Bill Gates said he would be fine with that. That should show you they are not in the game to take losses on HW.
They are fine with buying new studios and taking a hit on Gears 5 in order to push GamePass and xCloud, because that is where they see their future. Not subsidizing HW in order to sell more than Sony. In the end, Xbox HW is not a big concern for MS. On the other hand, PS HW is very important to Sony. And considering Sony has already said they want to have consumers move over as quickly as possible to the PS5, expect them to bring their A game on power, games, and price.