The more I think about it, the more I like having an immobile Phylactery Guard, rather than making some sort of jewellery that can be passed around like a bottle of Crown.
Even assuming the phylactery is small enough to be carried and harmless enough to not flay the flesh from your bones as you touch it, liches aren't the most trusting of people. They would consider letting anyone have their phylactery with the same cheer I would consider letting Stevie Wonder perform brain surgery on me.
If the ruler is really insistent, maybe they'll hand over a bauble:
"Here you go, my phylactery."
"Only a glass bead? Well you know how thieves are, if it was valuable it would have been stolen twice today already."
"The blood stained marble altar encrusted with rubies and emeralds, encircled with bands of platinum and menacing with spikes of turtle shell, radiating unholy energy that I have in the centre of my lair? It's, uh, a piece of abstract art."
"Why do I reform there instead of near my phylactery? Hmm... Oh, I know, being destroyed is a traumatic experience, so every time I reform, I instantly teleport there to relax a little. Soak in the atmosphere of my art gallery."
And just because the Phylactery Guard is destroyed, it doesn't mean the phylactery is:
Imagine a paladin, having fought through a horde of horrors, each one more horrific than the previous. He comes upon an altar radiating an aura of evil and uses his last strength to bring the Holy Avenger down upon it. Both sword and altar are annihilated and the lair starts to fall apart. Summoning energy he didn't know he had, the paladin emerges from the exit just as it collapses, having survived the last trap set by the lich.
Meanwhile, the phylactery is safe, having long since been buried in a deep hole under the altar, and the lich prepares for a short holiday, contemplating death, the universe and everything. The phylactery will resurface in a few millennia; someone will dig for treasure, or erosion will remove the soil, or something. Nothing stays buried forever.