I was using PureOS “Byzantium” on a Librem 5 USA as my sole daily driver for many years, but due to lack of updates from Purism, I eventually reflashed to Mobian stable, acquired a Motorola Moto G (2024) using CalyxOS, then migrated everything over to a Google Pixel 8 Pro using GrapheneOS. Before all of that, I was using a Alcatel Go Flip 3 with KaiOS. The only other mobile Linux distribution I considered with the Librem 5 USA but ultimately did not use was postmarketOS.
If you still want to stay in the mobile Linux ecosystem, I was quite satisfied with Mobian stable. My most used Flatpak applications were Lollypop and Shortwave, and I basically used the Librem 5 USA in Lockdown Mode as a music player. Even though 4G calls worked fine, I preferred user-empowered hardware isolation over involuntary connection, so for nearly all of the time I had the Librem 5 USA, I prevented anyone from contacting me over cellular or Wi-Fi networks under any circumstances.
Despite my experience, your mileage will vary, and everyone has different threat models, use cases and workflows. The Librem 5 USA accumulated many hardware issues over the years and my perspective of mobile Linux significantly changed throughout that time. Even if devices supporting mobile Linux are usable for now, there are many plaguing issues that remain unaddressed, and attempting to explain them thoroughly in this topic will significantly derail it.