Having a Linux distro on your phone could serve many different purposes.

Access to a different variety of software repositories. Using your phone as a server. Getting work done by connecting the device to a larger screen and using it as a desktop computer in a pinch while you are traveling.

Me though the appeal would be to have an entirely Linux powered operating system without the android ecosystem for increased privacy, security, and overall desire to not have to deal with all the bullshit anymore. With graceful root access.

I already have a custom android ROM and I am degoogled. However the ultimate step would be for me to one day get a Linux only phone, but I am not sure it is there yet.

Maybe in the next 2-3 years before I make that quantum leap, but I am looking forward to it.