Kind of. There is the PinePhone and Librem 5 that both run full Linux. I have a Pinephone. Unfortunately, the hardware is underpowered and the software is not ready to replace iOS or Android. The battery is also not good. The standby has improved a lot, so it can last a day of limited use, but the battery drains very quickly when the device is actively being used. It’s definitely fun to play around with, and it even has the convergence feature Microsoft tried to do with Windows Phone. The UI changes to regular desktop Linux when plugging the phone into a monitor and connecting a keyboard and mouse. But again, the hardware really limits what can be done.
In short, Linux phones are a thing, but not reliable enough to be the only phone a person has.
Brave is great for less techy people because it’s defaults are good enough. It’s not necessary to tweak settings and install add-ons to get basic privacy. I definitely prefer Firefox, but it takes some knowledge to get it to surpass Brave’s defaults.