I agree with your main point about disposability. There shouldn’t be many iPhones in landfills, though. Apple recycles 100% of the materials, so as long as the old phone can be traded in or dropped off in an electronics bin, it won’t be wasted even though the owner will have been out the money by rebuying prematurely.
In that report, they list iPhone 6 disassembly recovery by kg/100k phones (search for Tungsten.) Cross-reference with the components by weight for the iPhone 6S (6 is not available; see https://www.apple.com/environment/reports/ for all reports.) Ignoring battery, screen and plastic leaves .063kg/phone, and according to that side bar, Liam recovers .033kg/phone or ~50%. Assuming Apple recycles most of the battery, screen and plastic, they are recovering ~75% of each 6S. That's pretty good, and it's good to know that the unrecoverable portions are staying out of the trash (and hopefully heat/vapor waste is mitigated), but it's years away from being close enough to 100% to round up.
