Android shouldn't be considered Open Source anymore, since source code is published in batches and only part of the system is open, with more and more apps going behind the Google ecosystem itself.
Maybe it's time for a third large phone OS, whether it comes from China getting fed up with the US and Google's shenanigans (Huawei has HarmonyOS but it's not open) or some "GNU/Linux" touch version that has a serious ecosystem. Especially when more and more apps and services are "mobile-first" or "mobile-only" like banking.
That is a very hard problem, unless someone with serious name recognition like Linus Torvalds starts to lead that kind of effort, or a big company like Microsoft suddenly decides that putting 1 billion towards GNU/Linux would be in their interest. With small efforts, it will remain scattered.
Crowdfunding has a lot of power if there is name recognition behind the effort. Star Citizen has already gathered $800 million with mostly enthusiasm and a good start. Who is there to lead the effort for GNU/Linux phone development?
If anyone wants to give it a shot again, don't start with a GNU/Linux phone, start with something the masses actually will care about. Reverse-engineered, adversarially-interoperable social media apps for all the mainstream networks with no ads/dark patterns? Cool. Adblocking by default? Sure thing. Built-in support for a wide range of cloud providers (including standard protocols such as SFTP/S3/etc). And so on.
Address actual pain points that people have. "GNU/Linux" by itself does not address anything. The non-technical majority don't even know what that is or means, and even for technical people it isn't a perk by itself - sure, you can run whatever software you want... but you (or someone else) still need to write said software to begin with... or you could just trade a bit of money and "freedom" and buy an iPhone which doesn't have any of those problems.