I would agree that a Ph.D. and research does not necessarily make one a
good teacher of physics. But, it doesn't follow that it precludes one
from becoming an excellent teacher. Both as an undergraduate at
Berkeley and as a graduate student at Penn I suffered through some
classes taught by Ph.D.'s who simply could not teach, but at both
universities I also took classes from other Ph.D.'s who were absolutely
superb in the classroom (folks like Owen Chamberlain and Herb Callen
among others).
One thing that seemed to characterize the good teachers was their
attitude. They loved physics and the loved talking about it.