so perhaps Phil's scams no longer working is when he's a bit more older and his health problems get much worse then? Seems about right
Possibly, but only if it make him even more ornery or combative. If he has a genuine health scare expect to see an hour-long video about it in the same vein as when Leanna had her panic attack only with much more obvious begging. A gout attack, memetastic as that is, would probably throw a wrench in his plans as he'll be crabbier than usual. If he gets hit with Type 2 or something like that, though, he'll jump on that sympathy train in a heartbeat.
Personally I expect he's already been told by a doctor that he's borderline for
something stemming from his lifestyle and that's why he's floated the ambiguous "health issues" in the past to prime that pump. Whether or not he's actually gotten worse is immaterial, at least for his purposes. If something is wrong, he can claim it whenever he wants. I think it's just a matter of making the issue confirmed that's making him hold back. "Tax troubles" and "gonna lose my house, dood" are matters that he doesn't need to prove and don't require him to adjust his lifestyle to avoid scrutiny from his paypigs.
A health concern is another matter. He has to be
very careful selecting something if he's malingering, because many of them have symptoms that are visible, and all of them require a shift in lifestyle to some degree. He'd need to be more careful with what he drunkposts on Twitter, which is something I think even he knows he has trouble with, and the Instagram bragging about what he has for dinner would need to stop entirely, though it does seem like Kat has long stopped cooking for him.
Tl;dr the health scare saga would be a difficult one for Dave to write and I think he knows it. That's why he hasn't played that card yet.
Edit to add this: there's an additional concern to Phil bringing up a concrete health issue. Few things anger people more, or bring them closer together in the name of spite, than someone milking a disease for sympathy dollars. Want to see a cynic lose their shit? Let them find out that some douchebag on the internet is claiming to have the same illness his little sister has been suffering with for five years. Everybody has a loved one in their life who's struggling with something health-related so if Phil is going to fake something or, to a lesser degree, not take a genuine issue seriously while still asking for extra money for medical bills, he'd better be goddamn careful about it.