Argivian Phalanx — ruling 1

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Argivian Phalanx). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.

Argivian Phalanx — ruling 2

Argivian Phalanx's first ability can't reduce the {W} in its cost.

Argivian Phalanx : règles, fonctionnement et interactions (MTG)

Argivian Phalanx is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Affinity for creatures (This spell costs less to cast for each creature you control.) Vigilance (Attacking doesn't cause this creature to tap.)

How it works : Argivian Phalanx

Original English text — Wizards of the Coast / Scryfall

#1September 9, 2022· Wizards of the Coast
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Argivian Phalanx). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.
No other card is named in this ruling.
#2September 9, 2022· Wizards of the Coast
Argivian Phalanx's first ability can't reduce the in its cost.
No other card is named in this ruling.