I am a NJ resident working in Philadelphia. My employer only took out Philadelphia City Wage tax. No NJ state tax or Pa state tax. Am I allowed to take a tax credit for the Philadelphia City Wage tax?

No Philadelphia tax return is needed for this flat tax, but you cannot claim a credit on your NJ return.

You must file a PA return and pay that flat tax, and you can claim that yax ad a credit on the NJ return.