I will admit that "you can barely buy a sedan in the US anymore" was a bit of hyperbole, but certainly they have declined precipitously, from 80% of the US new vehicle market 40 years ago to about 25% today [0]. You can still buy sedans in the US, but not from american car companies [1].
Maybe small phones are like sedans, and the bigger and bigger iPhones are the trucks? Take this analogy where you will.