There are plenty of ways a PhD could be applicable to a surgical career, these are just a few:
-Many MD/PhD surgeons focus on a single organ system and test tissues extracted from their patients. For example, someone doing GI research may work as a surgeon doing primarily GI work and then test the excised intestine from their patients (with consent, of course)
-Some look at ways to improve surgical outcomes relating to infection, pain, rate of healing, etc. Granted, this category is more along the lines of clinical research, but you could imagine an MD/PhD collecting blood samples, etc from a patient, subsequently testing them for various compounds, and attempting to correlate the molecular biology with the clinical presentation.
-An MD/PhD surgeon may do research that requires them to have a specific surgical skill. For example, if an MD/PhD is an engineer who designs new pacemakers or surgical material, they may also train and learn to place them in an actual patient.