Sort of technically everyone on Android, and sideways sort of technically on iPhone, uses a linux smartphone.

Android is Linux based. iOS is based on a heavily modified BSD, which itself is a modified Unix.

If you're not crazy techy savvy, I'm not sure how much fun you'll have with a linux based phone, unless there's a strong community supporting it. Linux can be a bastard to set up and get working to your satisfaction.

All of these phones are currently developer toys. They are lean heavily toward that end.

For now, likely one of the android phones with a modded firmware toward security would be better.