First, Phil needs to start by rethinking how he talks to the people who supported him because it's irritating how he talks to the people who essentially gave him the opportunity to have the job that he does. In simple terms, being a streamer is like working in customer service. The viewers are your customers and if you treat them like horseshit, then don't be surprised when they start saying "Don't watch this guy, he's a cunt." Word of mouth is a pretty damning thing and if you're a streamer, it can be the death knell of your career.
Second, ignore the "trolls" and the like because by talking constantly about the problems you're feeding them. I think we're all hip to the fact that DSP wouldn't have even been a blip on the radar if he had just brushed off the trolls or hell, even engaged in self-deprecating humor with them (take his about face with FapGate because it got him views as an example.). Phil could easily take the wind out of their sails by simply mocking himself, but I don't think he's even willing to do that at times because he thinks it hurts him somehow.
Third, be open to change. There's absolutely nothing wrong with changing up things to break out of conformity and what have you. Businesses, successful businesses, do this all the time. To use a Let's Player, let's use TearofGrace as an example. Some of his earliest videos consisted of Halo trolling but eventually he started incorporating editing into all of the videos he made until he's left with something that can be genuinely funny for his viewers. Tear doesn't upload with nearly the same consistency that Phil does, but the videos he does make get a lot of views because they're put together with time and care. Phil just pumps out videos like it's the fucking ACME factory and most of them consist of dead air while watching him grind over and over again in the same areas, complaining about the same enemies and dying the same ways over and over again.
Fourth, Accountability. President Truman once had a sign on his desk that said "The buck stops here" meaning that as President he was responsible for the doings of his government no matter what and that he had to take responsibility for everything that happened under his watch. The same applies with Phil Burnell. If Phil wants to find someone to blame for his dwindling views, constant hate, or his demonetization storm from YouTube then he needs to look in a mirror. Phil could easily staunch this by simply making a video entitled "I'm sorry" and just apologize for being a massive tool. It would do quite a bit I think, of course this would have to be followed up with an actual effort to change for the better.
Fifth. Stop making promises you can't/won't keep. Super Mario Sunshine is just another feather in Phil's hat of broken promises. Rage quitting Patrons' choice games is honestly something that annoys me more than anything because you got paid to play these games. I'd play Hello Kitty Fun Time Island adventure if I was getting $1000+ from Patreon to play it and I'd act like I fucking enjoyed it even if I wanted to die inside. If I made an audacious promise like Project 7 to people, then I'd work my damnedest to try and pull off something for it. If I couldn't? I'd give back the pledges because I failed to deliver a product that others invested in. I wouldn't pocket the money and say "There's nothing I could do." while giving a halfassed apology and telling people to downvote the video where you made the weak ass apology to begin with...