On the wiring diagram of a telephone pole transformer on that web site:

The "black" and "red" (or L1 and L2) power supply cables that come into your house each carrying 120 VAC are connected to the low voltage side of the transformer. The white neutral wire coming into your house is connected to the center tap of the transformer.

The transformer converts 7200 VAC single phase power into 240 VAC single phase power, but the center tap is near zero voltage all the time and so you end up with "pseudo two phase 120 VAC" power. That is, single phase 240 VAC power that's been broken into two pieces, each 120 VAC, and each 180 degrees out of phase with the other.