I don't know what your native language is, could it be Swedish? In Sweden, media consistently write Iphone, because it's a name, and names start with upper case.
As you mentioned, what the marketing department says about the case of letters in the name does not affect this generic recommendation.
Of course, you'll find a lot of people writing it in accordance with the marketing style, bit typically you'll see media follow the Swedish spelling rules.
> In fact you wouldn’t really use iphone at all, but smartphone
The sentence "Smartphone is a phone made by Apple" (or maybe "A smartphone is a phone made by Apple") would have a very different and wrong meaning though, so that doesn't make much sense to me.
OTOH you would say Apple though, but I guess that avoids some obvious ambiguity