I don't think it's actually possible to cooperatively craft a lich's phylactery. The MIC rules for cooperative crafting say that each character involved has to supply "some of the prerequisites". But a phylactery only has one prerequisite, Craft Wondrous Item. Thus, if the rules are being followed in SoD, Redcloak is simply providing information and instructions to Xykon, but isn't actually participating in the crafting of the phylactery. Unless there are other rules elsewhere about cooperative item crafting that disagree with and supersede those in the MIC, Craft Wondrous Item should be added to Xykon's entry and removed from Redcloak's.