I think that this question should be closed because there are not enough details to provide a proper answer. The most upvoted one is based on the assumption that the item is casting the spell, but actually it is not clear from what the OP wrote.
I am new to D&D, and my DM is letting me play the Mystic, as long as I am not a butt about it. I have chosen the Order of the Immortal subclass, which has unarmored AC calculated like a barbarian, but cannot use a shield:
Immortal Durability
[...]
In addition, while you aren’t wearing armor or w...
@Eddymage I read "as per enlarge/reduce" as the same as the spell enlarge/reduce - which is how I think others have read it, too. Getting the full text would be better, but I don't think it's a close reason. But I wouldn't reopen if it gets closed without it.
@Eddymage That's what prompted the bounty on the spirit weapon "who is the attacker" question!
I think your answer is fine save for trying to have it both ways. Considering the caster the attacker, which is how we ended up doing it, it isn't automatically a critical. A spirit weapon attack made by a caster 30 feet away is somehow different than the attack made within 5 feet. Narration is left up to the DM.
Same with a ranged melee attack like a whip or an attack with 10' reach. Narration left up to the DM as to how this plays out.
"Leaving D&D: Things to Watch Out For" by vesper-of-roses. There's this tendency to view TTRPGs in a similar light: through the cultural lens of Dungeons and Dragons, a sort of "Latent D&D" if you will.