1. You can't fit a XXX billion param model on an iPhone. It's just impossible. A mixed approach where most ML is local; but some are cloud, fits with their existing Siri approach.
2. OpenAI won't share model weights, but if there's one company they'd make an exception for, it'd be Apple. Certainly not their big models, but perhaps they have a distilled, SOTA 3-7B model that they're happy to license, especially with Apple's Secure Enclave and ML model encryption.