Android runs toybox (or at least used to), which implements many of the GNU tools. But I think the complaint is that much of the userland to have a useful phone experience is proprietary.

If you could install all the GNU tools into AOSP Linux (probably not that hard), you still don't have a useful phone.

It's not even the desktop environment (think GNOME/KDE/etc.), as there is a good enough version in AOSP.