If you are billing physical therapy cpt codes then you only need to add the GP modifier. You may also want to look at the 59 modifier to see if it is appropriate for any of the codes you are billing. Some PT cpt codes are bundled together unless it is indicated that it was distinctly separate from the other services being billed for. If you are going to use both modifiers, I enter the GP in the mod1 field and the 59 in the mod2.
Michele