It says 120,000 to craft. Does it mean,that it is the item of 240,000 cost? So, the lich needs 240 days to craft it, right?
Assuming it follows the same rules for crafting, yes it would take between 120-240 days depending if the Lich used accelerated crafting.
Correct, what's interesting is looking over everything. It seems like you could also ignore the requirement of being 11th level by increasing the dc by another 5. Though it may be difficult to come up with that much cash even at 11th level, much less a lower level.
Does it have to be an item you create from scratch? Or could you do 240,000gp worth of crafting to an existing item? Could a sentient weapon become a phylactery?
Could a sentient weapon become a phylactery?
Possibly. There's no rule for, nor one against it. Ask your GM. Usually they're small boxes, or rings or amulets otherwise.
You do have to create it yourself though - no prefabs allowed.
Does it have to be an item you create from scratch? Or could you do 240,000gp worth of crafting to an existing item? Could a sentient weapon become a phylactery?
the description says something along the lines of "the typical phylactery is... , but it can be made out of rings, etc."
so, I would assume that yes it could be a sentient weapon. Though it does immediately bring to mind a plot point. What if the lich is just a sentient item since the wizard trying to become a lich screwed up the process and died a long time ago.
Then again, maybe that's what all liches are.
I was thinking that if a Lich chooses to place his soul in a sentient weapon, does the weapon now have a soul? It's not the Lich's personality, the weapon has its own personality and motives, but now it has a soul, it's not just sentient, it's alive now. Or is the soul just sitting in there and not available for use by the sentient weapon?