The idea is that because the manufacturer's costs also go up, there's no longer any reason for them to manufacture abroad, and the same goods are manufactured in the country instead. So while their prices are higher, the workers that make them are also paid more (and, perhaps more importantly, are paid at all, on account of having a job). And furthermore, that money remains in the economy of the country imposing the tariff. Ideally, the end result is that more people overall can afford that iPhone, for example, even if the sticker price is higher.

To what extent this works in practice is another matter. But I would posit that the notion that's common nowadays that tariffs are always bad is just as simplistic as wrong as the notion that tariffs can fix all problems. It all boils down to the specific numbers.