I've replicated this on 3 different phones and even on a USB wi-fi antenna I got in case my laptop's internal one stinks. I'm not the first person to ask why, but I might be the first one with a solid guess at the answer. And it isn't the known problem about device inter-operation – I've confirmed this across more than a dozen routers.
It's pretty strange, right? If there's one thing I've completely made up / guessed about signals, it's that big antennas work better, and the laptop just has much, much more space. And the USB one certainly didn't need to be worse than what they'd use in a phone. So why is it that I've had a years-long noticeable disparity between the two?
There are a couple guesses: (1) my laptop's OS uses Dumb Wi-Fi and my cell phone uses the same-ish hardware better / at higher power; (2) the laptop itself physically obstructs or interveres with the wifi signal; (3) the cell phone uses its calling-antenna and so it's huge; (4) or the router, seeing a cell phone MAC address, boosts its signals more to let the tiny device hear it (really, this is an umbrella theory of "environmental inequality").
So, how would I distinguish between them?
I notice tilting my laptop seems to help it get better signal. That's weak evidence for (2), I suppose. MAC randomization and spoofing doesn't help my laptop, essentially ruling out (4), although a covert I-am-a-cell-phone signal could be sent because of (1). (1) is pretty unlikely though, because I use Ubuntu on my computer and Android on my phone, and those are similarly made. A quick check rules out (3) – they use different frequencies and can't be interchanged.
So I guess my laptop is just too fat, and too consistently on top of big bulky surfaces like desks (where the phone has less internal material and is up in the air when in use). That's my best guess.
This post was saved by holding my laptop up in the air, as I lost connection with the server from the far corner of my bedroom.