I am a US citizen and will be go to Hongkong and Macau , from June 6 to June 11, 2016.

Dear Cristy, whether you need the entry permit depends on how you arrange the trip. If you fly from the US to Guangzhou, staying for less than 72 hours and then flying onward to HK or Macau, you can enjoy the 72-hour free transit policy. I personally think this is the best route for you because it saves the money and trouble to apply for the entry permit.

I forgot : I will be going to the Philippines first before going to Hongkong . I already bought my plane tickets .
Do I need an entry permit to go to Guangzou for 1 day from Hongkong ?

If you go from Guangzhou to Macau or another country or region, it's possible to use the free transit policy.