You call upon Orcus, the Demon Prince of Undeath, to transform your body into a skeletal thing, undead and immortal, and bind your life force within a specially prepared receptacle called a phylactery.
Lich Transformation is a 14th-level ritual.[DrMM]
At the conclusion of this ritual, you die, transform into a lich, and gain the lich template.
An integral part of becoming a lich is creating a phylactery, a magical receptacle containing your life force. When you are reduced to 0 hit points or fewer, you and your possessions crumble to dust. Unless your phylactery is located and destroyed, your reappear in a space adjacent to the phylactery after 1d10 days.
You must construct your phylactery before the ritual can be performed. The phylactery, which takes 10 days to create, usually takes the form of a sealed metal box containing strips of parchment on which magical phrases have been transcribed in your blood. The box measures 6 inches on a side and has 40 hit points and resist 20 to all damage. Other kinds of phylacteries include rings and amulets, which are just as durable.
If your phylactery is destroyed, you can build a new one; the process takes 10 days and costs 50,000 gp.