Question : How long are most people's visits to Phoenix when they fly in from Belgrade?
Answer : Of course you're not most people, but if you were, you'd stay roughly 41 days.
Question : If your plans are flexible, have you considered changing your departure day?
Answer : For the month of December, the cheapest day to fly is Tuesday. Flexibility is paramount when booking travel plans in order to keep costs down.
Question : Do prices fluctuate more for this route than others?
Answer : Prices for BEG to PHX do change a lot more than the majority of routes. However, the sooner you book, the better price you tend to get.