It's already a proper noun (not a pronoun!), but it's being treated almost as though the name of every individual Apple device is the product brand name, which is weird. Using a product brand name without an article is normally only done for uncountable/mass noun things like "gorilla glue" or many food/drink products.
I think of it as a “pronoun.” It makes it into a “person,” or some kind of major deal, like we call localities (usually) by their single pronouns. Sometimes, “The” becomes part of the pronoun, like “The Netherlands,” or “The Bronx.”
Usually, though, we assign pronouns (I’m not an English major, though, so the proper term may be different).
Like, you can’t have “a brooklyn,” or “an amsterdam.”
They want to make it so we can’t have “an iPhone.”