Eliae Darr
If a lich can create a phylactory, then why shouldn't it be allowed to make more than one? Granted, with several phylactories, there would be a distinct disadvantage in that the being's power would be split, but it would take much longer to kill it, particularly if the lich spread them out over a wide area.
As it happens, there is an epic spell that accomplishes this, which can be found in Champions of Ruin. Here are the details for it:
Aumvor's Fragmented Phylactery
Transmutation
Spellcraft DC: 30
Components: Verbal, somatic
Casting Time: 1 minute
Range: Touch
Target: One or more objects, including the caster's phylactery
Duration: Permanent
Saving Throw: None
Spell Resistance: No
Development: 210,000gp; 5 days; 8,400xp.
Seeds: transform (DC21), ward (DC14)
Mitigating Factors: field specialization (-5)
This spell can only be cast by a lich. It either separates the lich's phylactery into multiple objects or expands the phylactery to include multiple objects, as determined by the spellcaster. The number of such objects can be no greater than the caster's modifier for its spellcasting ability (charisma for sorcerers, etc.). Thereafter, destroying the lich's phylactery requires the destruction of the whole set of objects that comprise the phylactery. As long as at least one such object of the set exists, the caster cannot be permanently killed.
This spell can be cast repeatedly on a phylactery or part thereof. Each time it is cast, the number of objects that comprise the lich's phylactery can be increased by an amount equal to the caster's modifier for its spellcasting ability.
