Phil isn't necessarily to blame for the issues at MS. Though in saying that, he still owns every decisioj tjat passes through Xbox as a division, it's the responsibility he signed up for.
I mean, he's to blame in that he's made a few wrong bets. I think he thought Game Pass would be a service so enticing that it would cause people to migrate platforms for it, and that just hasn't been the case. Meanwhile Sony is making pretty traditional third party exclusive agreements like Final Fantasy XVI which are proving much more fruitful for the brand.
Some of it does seem out of Phil Spencer's control, though. They bought a LOT of studios, and even years later those studios just aren't delivering a massively strong output of marquee exclusives.
At the end of the day blah blah capitalism, blah blah CEOs aren't our friends, all that, but I do think Spencer is trying to his best to make savvy decisions that are enticing to gamers. But he's made some wrong bets, and some of the games just haven't hit the way they should have. Halo didn't hit, Redfall didn't hit, Starfield is more complicated but it can be argued that it didn't hit. Meanwhile games like Sea of Thieves and Forza Horizon are genuine successes, which is great, but those aren't really bolstering the Xbox brand