Why is it that he did so? Because his having to stay the course when his mother in law died turned him into one of the people howtheduckis thinking about when he talks about how most of Kool-Aid Nation reads the strip on a superficial level. Since he did what normal people do for Georgia and her family and since Elly makes plausible-sounding noise about helping Iris (and since he was in the midst of the Settlepocalypse and couldn't quite see that what looked like an extreme situation wasn't), he assumed competence and caring where none existed.
We also have to remember that Marian tried very hard to not be fussed over when her time came. As I remember, Elly had to remind Phil that their parents didn't really want to be taken care of by their children because they thought it was still their job to take care of them. The memory of both of his parents being rather lousy patients seems to also have lingered on. My guess is that when Jim was finally released from the living Hell of being treated like a child by a witless old meataxe whose response to his speech pathologist's broad hints that he was still in there was an indulgent grin and a honeyed slam against the silly girls running about pretending they can be competent (as well as how silly it is that they overrule a man who never saw him again), Phil thought that everyone involved did their best. The sad thing is that he'd be right!!