If carrying a firearm in a vehicle, whether open, concealed, locked away in a glove box or in bits and pieces inside the spare tire, you must possess a License to Carry Firearms (LTCF). Unless you're going directly to or from a range and your house, or to or from a firearms dealer, them's the rules.
Once outside the vehicle, you can open carry to your heart's content. You've got an LTCF (you needed it for the vehicle carry), so you're good to go in Philadelphia or anywhere else in the Commonwealth (except in certain government buildings, courts, schools and state parks (concealed carry with an LTCF is okay in a state park).
The biggest hurdle you'll have to overcome will be that you're driving a company vehicle. Does your company specifically prohibit employees from carrying firearms? If so, you've got a choice - possibly lose your job or possibly lose your life. If no policy exists, you can either carry without asking permission, or you can ask for permission (it's their vehicle, you're their employee, it's their potential liability if anything ever goes wrong).