Domain of Undeath

After years forming a bond with the undead, you have thrown away basic cleric knowledge and worship, for they never truly understood what lied in the dead. Always focused on keeping life or keeping death they never considered looking into worshipping undeath. But you have.

Creation of Undying Servitude (3rd level)

As an action, you may expand a use of your channel divinity to summon an undead creature, as your knowledge and worship of the undead haven't gone unnoticed. This creature depends on the number of levels you have in this subclass. It lasts for 24 hours, during which you may use this feature to increase the amount of time it lasts by 24 hours. 
At 3rd level you may summon an Ogre Skeleton (CR2)
At 7th level you may summon a Mind Drinker Vampire (CR4)
At 13th level you may summon a Skeletal Knight (CR7)
At 18th level you may summon an Iron Ghoul (CR5)
You cannot have more than 1 undead this way. If you have a charge of channel divinity while the undead is active, you may expend it as an action to heal the creature to full, or, if it has died, revive it with 1 hit point. The undead is an ally to you and your companions. In combat, it shares your initiative count and takes its turn immediately after yours. You may use a Bonus Action to command it to take an action on its stat block, or some other action(no speech required). If you don't issue the undead any commands, it takes the Dodge action and uses its movement to avoid danger.

Good servants get power! (6th level)

As a bonus action you may expend a spell slot to empower the undead under your command. This feature may only target undead created by your channel divinity feature or creatures created by your necromancy summon spells that summon a single creature. You may target both when you activate this feature, should you have both. As you level up, they gain additional benefits as well, as you learn to harness the full prayer of undeath into your summons.
At 6th level they gain a bonus to hit and damage equal to the level of spell slot expended.
At 9th level they may add the level of the spell slot to their AC and the DC of their saving throws if they have a feature that does requires a saving throw.
At 15th level they may add the level of the spell slot to their Saving Throws, and at the start of each turn they gain an amount of temporary hit points equal to the spell slot expended times half your cleric level, rounded down.
These benefits last 1 minute after you activate them, ticking at the end of your turn. (For avrae purposes, code should read as 11)

The power of undeath, the power of a lich! (Level 17)

Once per week (IRL) you may create a phylactery. You may only have one phylactery at a time. While you have this phylactery, if you would die, you may instead be reborn at your phylactery. This phylactery cannot move, and must be a physical object, it cannot be an idea, or a creature. You're body and soul and all items on you at your death are recreated within 30 feet of where your phylactery is. If any items require attunement, you are automatically attuned to them as part of this process. You are treated as if you had the spell True Resurrection casted on you, but the negative bonus does not decrease as the days pass and the number of IRL days is 3 instead of 4. Creating a new phylactery destroys the old one, and using the phylactery renders it unusable for 1 IRL week. You cannot create a new one within 1 IRL week of it's ability being used.

If your undead dies and you do not revive it, you may choose to have your phylactery revive it instead (assuming you have an active one), requiring all charges of your channel divinity (including any given by items) to be available, and you must expend them all. Reviving your undead this way brings it back to full health points, and does not expend your phylactery's use.

.Expanded Spell List

You may add the following spells to your prepared spell list, not counting against the number of spells known. You gain the spells at certain levels (!sb add on avrae, cannot add them normally)

3: Wither and Bloom, Spare the dying
5: Speak with Dead, Summon Undead
7: Blight, Spirit of Death
9: Negative Energy Flood, Raise Dead
11: Soul Cage, Circle of Death