Nope. It's not required for an instructor to have a PhD in order to teach. There are a few classes at my program in Houston that have instructors without PhDs, granted that they are pretty well-respected in their fields with other certifications (OCS, NCS, FAAOMPT, CHT, OT/PT, etc).
The PhDs teach mostly the harder and more advanced classes, rather than classes like Basic Skills in PT, or Primary Care in PT. There is an advantage to having PhDs teach these classes, as many of them have a deeper breadth of knowledge in the areas they teach. However, this is wholly dependent on their
quality of teaching. lol. One of my professors, who just retired at the end of last semester had been with TWU for 26 years or something, and he is brilliant, especially in the field of neurology and clinical electrophysiology. BUT, his teaching was just... let's just say his lectures and exam questions were totally "wtf is he saying/asking". He was funny though.
I'm not sure how the DPT/PhD programs work in Ohio, but here at TWU, we start IRBs, our study, and whatnot during our DPT curriculum, take PhD classes in addition to our DPT classes if we want, become formally accepted into the PhD program upon graduation and licensure, continue PhD classes, work on our dissertation while working in the clinical setting. Then somewhere between 3-10 years after DPT graduation, we get our PhD. I don't know what I was thinking.
The acceptance process was pretty tough, too. They accepted only 1 from my class for the DPT-PhD program. And ALL the professors are in a meeting room interviewing you and asking you questions, in addition to a 2 minute "speech" from you. And they have all your transcripts, grades from the first semester, professor opinions and inputs on your performance and capabilities, the essay your wrote for the application, and your resume. Lol. This fall, I start writing my IRB for my study, which is TBD until I meet with my research advisor.
So, it is possible! Just really think if you reaaaalllly wanna do this. =]