You can sell your iphone without any issue, there are plenty of stores around me offering to buy used models to resell. I'm actually contemplating buying a used model. Can't do that with steam games.
I'm also pretty confident that if apple and their services disappeared tomorrow, my iphone would keep on working just like it does today. Sure, no more updates, no more new apps, it would be frozen in the state it's in.
Therefore, I think the question is whether an iphone is a "general computing device", or "an appliance". I can see the arguments for both, even though I tend to treat mine as the latter.