The phone just becomes the processing power; essentially an ARM laptop with all of the peripherals external.
I currently using Pixel 9 Pro XL (512GiB) and I imagine it's got more compute power than my ageing 2019 XPS 13.
Conversely, I'm not entirely sure what the use-case is. It couldn't replace my work-laptop with a 20-core CPU and 64GiB of RAM and ARC GPU, running Ubuntu/Gnome that I can also connect to a couple of monitors, keyboard, mouse, speakers, webcam, and more with a single cable via a docking station; and if I was going to carry the peripherals needed to do this with my phone, when on the go, I'd just carry a laptop, like I do now.
Curious to hear what the use-case is for people with these desktop/phone crossovers. If it's to cover the use-case where I haven't brought a laptop with me, forgotten it, didn't bring it for weight or whatever; where am I supposed to find these peripherals to use?