As history also teaches us, he does so at his peril. This is because he doesn't seem to notice it but each and every time they interact for any great length of it, it's obvious that she's trying to drag him down to her level. If she doesn't want to get into a pointless, frustrating row over how she's owed this, that and the other thing because he supposedly came along and stole her childhood, she's trying to resume her role as "Big Sister, Irritating Dispenser Of Stupid Advice And Also Betrayer Of Confidences For His Own Good And Also To Her Own Advantage." Again, Phil is only dimly aware of this because it doesn't make sense that a grown woman would behave as if she were trying to get Mom and Dad to cut off his allowance for something they can't actually do much about.
What this tells me is that Georgia made a point of separating them because unlike everyone else in the strip, she remembers what a dangerous influence Elly is. Phil came damned close to finally telling Elly off and hammering home the fact that she's a spoiled brat who lives to make conflict and generate tension because she thinks happiness is bad and wrong but didn't quite reach the target. Georgia realized this was futile and did the next best thing to the conflict resolution Elly doesn't want because it means admitting that she is the chaos she's been fighting: keeping the two of them at arms' length.