Flight question
 

I was wondering why would a flight from SFO-MNL stop in Guam on the way but goes n/s on the return? I doubt it's for re-fueling. It's 6900 miles and you can fly SFO-SYD n/s or EWR-NRT n/s. Anyways for the 45 minute layover can I get off the plane since Guam is in the US? Would I be able to book Phillipine Airlines SFO-GUM spend a few days there and go to MNL and returning without a stop?