Not entirely true - a growing number of PhD-holding faculty have labels like "lecturer" or "instructor", which are non-tenure-track and often contract based. Like in the public college system, this is leading to the majority of student contact hours being from faculty who don't have any permanent status within the university, and whose pay is far below even the junior professors.
My University also has a few other titles: Acting Prof, Research Prof, and of course Prof Emeritus