While it's not as Constructed-playable as the common Ajani's Presence or the rare Launch the Fleet, it's a cool card to consider if you're playing a casual Heroic-themed deck. Especially in Commander, where mana is plentiful, Phalanx Formation can serve as a finisher.
The best example of this being played in Constructed is in a Blue/White Heroic deck, which would include the blue creature Battlefield Thaumaturge. The Thaumaturge reduces the casting cost of a spell that targets by one colorless mana for each creature that spell targets. Therefore, the Formation costs only 1W to target one creature, 1WW for two creatures, and so on. It's considered "jank" by most players, but if you're dealing with a Heroic deck, it's one to watch for.