(Strip Number 4575, Original Publication Date, 3 March 1986)
Panel 1: As his dozy big sister gets the instruments at the ready, Phil tries to explain the importance of dental work to a trumpet player; it's a big day because no one in his line of work wants to have anything done to his front teeth.
Panel 2: He then says that if John changes their shape even to the least degree, it could
Panel 3: He sets up the punchline when he gets all desperate about how he can't afford it if there's a mistake.
Panel 4: Rock God-Damned Stupid Elly smiles and tells Phil that it's all good because John fixes relatives for free because the dumbass misinterprets this as a concern about the dental bill and not his loss of livelihood.
Summary: Trying to explain the real problem to her would be something of a non-starter because to her, afford means only the one thing. Also, he'd be better off if he didn't play discordant noise she can't sing along to anyway and worked an honest job and thus had enough to actually afford dental care.