Question : How long are most people's visits to Phoenix when they fly in from Medford?
Answer : Of course you're not most people, but if you were, you'd stay roughly six days.
Question : If your plans are flexible, have you considered changing your departure day?
Answer : In February, Friday is your cheapest day to fly. Flexibility is paramount when booking travel plans in order to keep costs down.
Question : Are prices changing frequently for this route?
Answer : Flight prices for MFR to PHX change a lot more than most. However, the sooner you book, the better price you tend to get.