I am in thailand on a 60day tourist visa and want to go to Cambodia when I leave thailand I will still have 20 days left on visa . Can I get 60 more days at the thai embassy in pp .

You could get another tourist visa there. It can take up to 4 days to get it unless you use an agent.

You may need to show a ticket out of the country in order to get it.,

If you are just making a short trip you could apply for a 30 day extension of your 60 day entry and then get a re-entry permit that would keep your permit to stay valid when you return.