The margins get really thin after the first 2 billion or so. Middle income globally is ~10-20 PPP dollars a day and that's only ~17% of the world's population. They're generally radically different phones between markets too no one's really dominating the cheap phone market.
The margins are only thin if you're used to 40% as Apple has been. They're not at all so thin that the rest of the pack aren't making actual profit filling the gap for the other 7B people who aren't well off westerners.
https://www.pewresearch.org/short-reads/2021/07/21/are-you-i...