Makes you think: imagine buying a laptop that is just screen, keyboard and a trackpad and slot your phone into it for a bigger device.
Similar setups have been tried unsuccessfully. There are many factors that would make such a device a mess, IMHO:
1. USB-C would be a bottleneck for performance, so either you need to add costs and complexity by either adding another port or Thunderbolt in an attempt to boost performance.
2. By the time you add storage, screen, webcam, etc. the cost of the device would probably be close o what one that had the A18 or whatever in it anyway and not need the added cost of a phone.
3. If you try to do everything on the phone such as enough storage, graphics, etc. that would drive up the price of teh iPhone and impact sales to people who just want an iPhone. A specialty iPhone for such a device would likely be a niche product not worth making.
4. From a marketting perspective, it begins to blur the iOS/iPadOS/MacOS boundaries, something Apple has studiously avoided.
5. Battery run times could be an issue as well, as you'd need to charge the iPhone which has inherent losses impacting how long the device can run on battery power. If you didn't but just powered the iPhone without charging the iPhone size would limit battery size, and if you used the iPhone battery without charging you risk a dead laptop and phone at the same time.
I personally think we would see an iPad running MacOS before we see such a device.