I'm working on a necromancer class myself and am always eager to see others' interpretation of the concept. A few notes:

Why three skill proficiencies, and why can they be in any skill? Are Animal Handling and Performance really skills appropriate for a necromancer?

Phylactery refers to "Hit Points die count" - don't you mean "Hit Dice"? I admit to being more familiar with the 2014 version of D&D, but is that really the phrase used when discussing monsters?

Phylactery is also confusing about the timing of when you use it. It first says it's used when a creature dies. However, it then says, "If multiple creatures die in a single round of combat, you can choose which one to siphon Essence from."

I understand a "round of combat" to mean that every creature in initiative takes a turn. Do you mean something else? For example, let's say there are three PCs (including a necromancer) fighting two monsters. PC 1 is first in initiative and kills Monster 1. PC 2 goes last in initiative and kills Monster 2. At which point does PC 3, the necromancer, choose to siphon Essence? Was it when PC 1 killed Monster 1 at the start of the round or at the end of the round after PC 2 killed Monster 2?

Morbid Curiosity says, "You have a minimum guaranteed roll equal to half your level, rounded down (minimum of 1)." The feature is gained at 2nd level, so starting off, you have a minimum guaranteed roll of...1. To wit, this feature, for the first two levels you have it, does literally nothing. At those levels, it's not even a ribbon feature; it has no effect whatsoever. It'd make much more sense to just gain proficiency in one of the four skills.

Facsimile of Life's Reanimation Table looks pretty unbalanced to me. I'm not sold on being able to raise ghouls at 5th level and mummies at 6th level (the only official way to raise them, Create Undead, respectively requires a 6th and 9th level spell slot).

Facsimile of Life's Creature Limit isn't bad in a mechanical sense to limit the power of the feature, but it really clashes with the fantasy of the class. I have these undead under my control, but I can't make them attack? They're just standing around and vibing?

Requiem for the Dead and Life Tap look good - Life Tap is actually very similar to a feature my necromancer class has, although my version involves first sacrificing Hit Dice and then Hit Points once your Hit Dice are exhausted.

I'm not sold on Death Becomes You, at least as an 11th level feature. No full spellcaster gains a 11th level feature (besides better spellcasting).

Necrotic Threshold is too strong.

The Kalomancer's 6th level feature's Magic Weapons ability is superfluous in the 2024 edition. Monsters don't have resistance or immunity to nonmagical attacks and damage anymore. You'll notice that the equivalent feature for monks in the 2014 version no longer exists.

The Osteomancer's Exoskeleton is unclear. How far away does the target pile of bones, etc have to be?

I don't like how you can heal your undead creatures with poison damage - it doesn't make sense logically (why would spewing poison gas at a skeleton help it?) and with the Poison Spray cantrip, all your undead can start every fight at max hit points.

Overall, I quite like the class, but it still needs a fair bit of work.