1. A Lapdock (dumb screen, battery and keyboard in a Laptop form factor is still about $300), more than the base PineBook Pro
2. A Phone can be easily carried, far more than a Laptop.
3. A Phone that can function as a computer makes it easier to carry the tools and data you need with you.
4. Sometimes having multiple computers can be more convenient than a single machine. Like with video editing, sound engineering, large databases, programming etc.
5. Being on the phone while working on a laptop is more convenient than a single device that you have to configure with either a bluetooth headset or similar, just to take a call while it’s docked as in it’s laptop housing as you suggested.
6. I’d be willing to allow my kids to use my laptop, but not my phone.
7. Having one device on a VPN while the other is on the clearnet can be helpful for troubleshooting.
8. Having two sets of separate data can be helpful. Like “Laptop Mode” for work, and “Docked Mobile Phone” mode for personal.
9. Having a separate phone and Laptop makes it easier to do thinks like use your laptop for Presentations, and using your phone as the remote controller (a la. KDE Connect).
The reasons are plentiful if you look for them 😁👍