Curious, aren't phones and tablets essentially just smaller personal computers?
they are not the same thing
they do less; the software is restricted, especially on iOS, there are _rules_ set out by the manufacturer about what is acceptable in software on the platform, both thematically and functionally. An app generally can't interfere with other apps, it can't be a dope wars style game about drugs; there are a lot more caveats, but I am far from aware of them all. For a long time you couldn't get a compiler or interpreter on iOS, so you couldn't use your "computer" to make more software... so it wasn't general-purpose at all, since you by definition couldn't change its purpose without the ability to make new software.
Phones and tablets are great for consuming certain types of content, and having a portable camera with networking has enabled a lot of content creation. But a phone isn't a great device for doing something like long-form writing.
But iOS is not a phone. Windows could set rules about what was acceptable on the platform, but that wouldn't change what a personal computer was. There are no rules about what's acceptable on an iPhone.
so iOS essentially is the phone, since there are no iPhones without it. It's not like you can just pop in an SD card with Linux on it...