Once per turn: You can change this card to face-down Defense Position. If this card is flipped face-up: You can destroy monsters on the field, up to the number of other "Geargia" monsters you currently control.
Yugioh is a game where wording is extremely specific and extremely important. Select is not the same as Target, for example, despite both being basically the same action. And then there's Discard as Cost vs Discard as Effect.
In Geargianchor's case, it destroys multiple cards at once, so it doesn't target, even if you can select which ones to destroy in case you can only destroy 2 out of 3.