This is the method stated in 2e Ravenloft suppliment "Van Richten's Compendium 2: Ghosts, Liches, and Ancient Dead.
Constructing the Phylactery:
The initial container (whether it be a small box or jar, a hollow ring or amulet, etc) must be at least masterwork quality and worth at least 1500 gp. The lich themself must etch various magical symbols on the internal surfaces of the container, which are then filled with silver. The symbols must include both arcane symbols of power (likely necromantic) and the wizard's personal sigil.
Following this the following spells must be cast upon the container:
Enchant an Object (likely an item creation feat in 3.5e rather than a spell)
Magic Jar
Reincarnation (perhaps a researched undead variant?)
Permanency (perhaps once each on the Magic Jar and Reincarnate spells rather than singly at the end?)
Only following this is the item suitable for use as a phylactery, but only for the use of the wizard that created it.
It is suggested that perhaps an uncommon time or rare astronomical event might be necessary while the spells are being cast - midnight on the winter solstice during a new moon, for instance. Or perhaps merely during a new moon or on the winter solstice. Or perhaps only when a rare red star / planet is ascendent or when a comet moves across the sky.
Constructing the Potion of Transformation:
The Potion of Transformation should be its own problem. It should require at least one skill check (possibly multiple in the style of complex checks in UA) as it is suggested that if even a slight error is made death could result - or worse.
The ingredients come from a variety of poisonous substances and venoms, natural and otherwise: arsenic, belladonna, nightshade (isn't this redundant? aren't the prior two the same?), heart's worry, and the blood of various venomous creatures such as wryverns, giant scorpions, serpents, etc. Finally, the potion requires a heart from a sentient being. (Thus the 'unspeakably evil' bit, I guess, although I note that the it doesn't state that the heart can't be donated by one willing to aid, and in pre-3e liches could be non-evil, such as those elven liches in FR.)
Once the ingrediants are all properly mixed the following spells are cast upon the potion:
Wraithform (gaseous form?)
Cone of Cold (maybe another cold spell?)
Feign Death (??)
Animate Dead (maybe Create Greater Undead?)
Permanency (again, should it be used on each or once at the end?)
The potion should be drunk at night, and while it suggests during a full moon, I tend to think a new moon is better themantically. It states that upon consuming it the wizard should roll a System Shock check. I would guess that a Fort save vs Massive Damage is the 3e / 3.5e equivalent.
If the checks fails the wizard is worse than dead. They can no longer be raised or returned to life (or unlife, or any form of playability) - even with a Wish or Miracle, although I suspect that an evil deity of undeath might be willing to bend a few rules (of reality). Actually, it states that only the direct intervention of a deity can resurrect one killed in this manner.
Success leads to lichdom.
Maybe you can get some ideas from the above description, at least a bit of flavor, if not mechanics. It seems like it would require Craft Wondrous Item, Brew Potion, maybe another feat specifically for creating the phylactery (Craft Phylactery, maybe?), and several spells. I would likely expect Spellcraft and Knowledge (arcane) checks while gathering the information for the ritual and brewing the potion. The player would not know whether or not they succeeded until the consumed the potion, of course. They would just roll and state the results. Also, quite a few spells would need to be known, and the GM would have to allow Permanency apply to spells typically not allowed. The cost in XP and gold for such, however, would likely equal or exceed the costs stated in the Lich template for crafting the phylactery, I imagine. If not, just up the costs for the masterwork container or add more spells needing cast upon it with permanency applied. Don't forget the costs - in money or in time / quests to gain all those rare blood and venom samples. Lastly there is the heart. Perhaps it must be from a specific type of being (same race as the wizard maybe, or devoted to a deity enemical to undeath perhaps).