The US is SINGLE Phase to most residential home unless it a special set up.
Its split leg , some might say split phase not two phase.
I remember in college we learned that there was one two phase system in operation and it is a few gov buildings in part of Philadelphia if I remember correctly. That's was in the 80's, but I think that system may still be working. It was 100 years old in 83 when I was in school, again if I remember correctly. I also vaguely recall Tesla working with a two phase system in the 1880's and Niagra falls using it, but as of right now we use single phase and 3 phase in the USA.
Someone smarter than me can put it in simpler terms I am sure.
The following applies to North American electrical systems....
Two phase is not the correct terminology and sometimes, the terms "split phase" or "split leg" is used. The 220 power that we are familiar with is what comes into our home service panels and it consists of one neutral and two "hot wires". Somewhere in the neighborhood, there is a transformer with high voltage coming into it. They put a winding next to the core and it induces 220 volts into the winding. The two wires from that winding are the two hot wires that enter your house. If you measure the voltage between those two hot wires, it will read 220 volts. In the middle of that winding, they put a "center-tap" which is just a wire that connect to the center of the winding. That wire is the neutral that is brought into your house. If you measure between the neutral wire and any hot wire, the voltage is 110 but, one with respect to the other is 180o out of phase. Without a significant description of phasor mathematics and something called "complex numbers", it would be very hard for me to describe in other terms why the phase change occurs but, suffice it to say, it does indeed occur.