Fairphone provides a version with a de-Googled Android (/e/OS) and I think that enough for people who care about their privacy and don't want to share their data with Big Tech.
Having an actual Linux phone with the same userspace as a Linux Desktop is cool, but it's even more niche.
It's definitely niche, but the exclusive features can be useful to quite a few people I believe: https://source.puri.sm/Librem5/community-wiki/-/wikis/Freque...
Not a competitor without a dedicated software developers team: https://news.ycombinator.com/item?id=37914312.
All others don't offer GNU/Linux phones.