Don't always assume that the goal is to prevent the phone from being sold cheaper. High demand items may also merit a higher price and Apple may want to keep the price artificially low.

https://en.wikipedia.org/wiki/Price_fixing

"In neo-classical economics, price fixing is inefficient. The anti-competitive agreement by producers to fix prices above the market price transfers some of the consumer surplus to those producers and also results in a deadweight loss."

It also send invalid signals into the economy about the value of an item that may create bubbles or unreasonable expectations for low prices that are unsustainable (and therefore anti-competitive).

The Diamond trade is a very good example of price fixing where otherwise plentiful and cheap stones are controlled on the supply-side to keep prices artificially high.