Ph.D.-ed philosophers vs Doctors of philosophy vs philosophy Ph.D.'s?
To expand upon @MattSamuel's comment, any/all of the following probably work:

I work with...


...a group of philosophy Ph.D.s
...a group of philosophers with Ph.D.s
...a group of doctors. Doctors of what you ask? Philosophy.
...a group of philosophy researchers (ed. note: tends to imply Ph.D.s, but not explicit)


The simplest option in my opinion? "This is Dr. X, Dr. Y, and Dr. Z. They all study philosophy."