You shouldn't expect the usefulness of devices to be linear in cost, even for completely rational buyers uninfluenced by fashion or culture. Such buyers will select a phone where the marginal cost is equal to the marginal benefit.

Water gives my 99.9% of the usefulness of Coke (i.e., I don't die of dehydration), but it's also very reasonable for me to spend 10 times more for Cokes because the marginal cost is still small compared to the enjoyment benefit.