Just did a few minutes of research and what I originally thought is correct. 3 phase power is what is needed for large motors and is not needed in normal household use unless you have a machine shop or large welder in your garage.
Reading an article on this site discusses the issue of 3 phase power at RV parks. Look at the section titled "Update" towards the bottom.
RV Electrical Safety: Part III – Outlets | No~Shock~Zone
The labeling on your coach basically means you can use standard household 2 phase power or 3 phase power used in RV parks which is now code compliant.
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