Adding a dedicated RV power plug. What would you do?

I'm leaning toward the 20/30/50 install. I'm not an electrician but know enough to be dangerous. And, no I'm not doing my own install but really want to understand the one thing that keeps popping up in the descriptions, "single phase". It's my understanding that 240v is simply two 120v legs that are 180 degrees out of phase. Doesn't that mean "2 phase"?