But it still contains a cellular modem and a wifi module, both of which run proprietary firmwares.

But, crucially, they both run externally to the CPU and main system, and can not affect it in any way. It’s just as if they had put the firmware on a ROM chip beside the modem and wifi chip.

A phone, sure, a smartphone, not a chance

The Librem 5 is absolutely a smartphone: https://puri.sm/products/librem-5/

Your linked page calls it a "phone" not a "smartphone", so you're proving GP's point.

What. By that definition, the Google Pixel 5a is not a “smartphone” either, since its product page does not use that term, either: https://store.google.com/us/product/pixel_5a_5g?hl=en-US

Your leg is being pulled.

*plonk*

By what metric is it somehow not a smartphone?