No contract phone

I will be in Cambodia for a month.  Is it possible to buy a phone just for local calls?  Where and how much?

Yes, just simply go to any phone shop and get your self a phone and a sim card.  The price of a Sim card can vary from $1.00 on up depending on the number you get such as a lucky number etc. and if you register your number.  Most likely you will need Identification such as, passport etc.  They will show you a list of numbers to choose along with the provider (smart, metfone, cellcard, etc. etc)  and on the side of each number there will be a price for it.