220v isn't achieved via two phases; we get 110v out of a single phase by center tapping the transformer. The center tap wire is called the "neutral" and is at ground potential, and then the two "hot" wires. There's 110v between the neutral and either one of the hots, and the hots are 220v apart. It's still one phase.

Note I used 110/220v here and 120/240 above. peak-to-peak, root-mean-square, ask an actual electrician, I'm just an asshole on the internet.