How do you get a pure sample of phosphorus?
You need an electric furnace to obtain pure phosphorus for phosphate rocks. Also, permits are required in some areas to buy pure phosphorus from stores because it is a highly reactive and toxic nature, especially white phosphorus. It rarely occurs in free state.
Mix the phosphate rocks with coke and sand and when it is heated in an electric furnace, phosphorus vapourises out and can be obtained by solidification thorough cooling.
Warning: I hope you are asking this just for knowledge or for a school assignment because of the high level of hazard associated with the process. Even if you do get an electric furnace, do not try to make this highly dangerous element.