Man, I was wondering about this myself, as a guy with 10 years in the phone firmware business
I don't think Musk has any realistic chance of competing with Apple. Apple has been poaching from the best of the best in every level the phone industry for over a decade now.
He could quickly and effectively crank out an undifferentiated Android phone for sure, but I'm not sure what he'd do with it or how he'd convince anyone to buy it. His phone would be more expensive to make than the ones out of Moto, Huawei, etc, and it wouldn't work as well. Maybe if he hired aggressively or borrowed people from Tesla somehow he could make a good Android phone, but I don't see why anyone would buy it.
I actually thought that by now we wouldn't really be bothering with apps so much, and computers would be more like the one on Star Trek. I don't think Musk could just toss that together any time soon though, haha.