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.
Phil didn't have the power to decide much financially until his promotion in 2017 I guess. That's the important date which gave him much more power about how to use which amount of money.