(Original Publication Date, 28 May 1991)
Panel 1: We find ourselves watching Mike spend a heck of a lot of time on the phone. This is signified by Lynn showing him in various poses with the receiver pretty much tack-welded to his right ear. From left to right, we have "Mike talks on the phone", "Mike boasts about something", "Mike opens a can of soda", "Mike laughs at something the caller says", "Mike listens to what the other person says", "Mike drinks more soda", "Mike listens to whatever whoever is saying" and "Mike probably arranges to meet up with Miss Dangerous Outfit in the hopes that she's wearing a sleeveless top so he can at least see a hint of brassiere."
As howtheduck says, Lynn was trying to show off but her limitations made her substitute "screwing around with a can of store-brand cola" for a facial expression.
Panel 2: When he gets off the phone, he complains to John because for a reason he can't understand, his ear hurts.
This neatly parallels Elly getting shoulder pain because she's too stupid to switch shoulders when she spends a lot of time on the phone.
Summary: This is because he's being used to nag Aaron about spending God alone knows how many hours talking to God knows who when the phone is 'really' for the person who pays the bill.