In North America, the two halves (each 120 V nominal) are NOT out of phase. They are simple the top and bottom halves of a center-tapped transformer sitting outside on a pole or in a big green box on the ground. Go outside and look at it. The power company gives you one wire (plus a ground) to their transformer and two (plus a ground) leaving it going to your house. The coil on the half of the transformer facing you is tapped to ground ("earth" in non-American English) in the center with nominally 240V across the whole transformer, and 120V on each wire. This has nothing to do with phase. The other side of the transformer (facing the line) has at least 7000V (or as much as 45,000V), and is tapped on one end - with the other end going to a SINGLE WIRE for a single phase from the power line. If you see three wires plus a fourth one below, you are looking at three phases, but unless you are in an industrial setting (Lathes, BIG welders, mills, data centers, etc.) only one wire comes into your home or apartment building. If there are three phases going into a building, you will see three transformers on the pole or poles. Look at it and see - all the outside wires are exposed and you can photo them with your phone from the ground and zoom in to trace the wires.
Once inside, the breaker box, or panel or sub-panel will have a main breaker (kills all the other ones). The number of Amps rated on that main will be the 80% of the max loadable Amps at 240V (nominal) and the total Wattage is that number times 240V. In other words, if you follow this so far, you can fully load TWICE that many amps at 110/120V - assuming constant load and even distribution across smaller breakers. Note also that every breaker (by code/law) has 20% leeway between the label and the actual trip amperage, (again, don't trust me, pull one out and look at the label on it) so if you have 200Amp sub panel for your house or condo, you might be able to get 440Amps of 120V equipment loaded before things start to smoke. Keep in mind, mfg tolerances, age, loose screws or push connections, etc. AND, while you are reading the 20%, etc on the side of that breaker, you will note that it will have been made in Mexico at a location in a state that does not enforce a minimum wage or allow effective union negotiations - so figure that into the tolerances. In other words, if you push it anywhere close to the maximums, you should not sleep where you mine, and you should have good fire insurance - especially the liability portion.
25 years building data centers.