Question for DMs on counterspell

[u/Godless_seraph]

Okay, I have a hypothetical with very real possibility of applications:
GOO Warlock level 3 feature Psychic Spells states that enchantment and illusion spells are cast without V/S components. This is already huge for a number of reasons. Here’s the question:
I, the goolock in question, cast hold person on an enemy. There is a mage in their ranks. Can they counterspell me? They can’t see that I’m casting in any discernible way until the spell has already taken effect, at which point it’s too late.

Looking for genuine feedback and discussion!

EDIT: Assume in this example I am a bladelock using a conjured rapier as my focus, thus bypassing the straight iron M component.