Three different things with two lines and a neutral:
2 phases and neutral from a normal 3-phase 4-wire distribution system - most often found where old 3-wire DC underground cables were reconnected to a 3-phase 4-wire supplies and might be upgraded to 3-phase by replacing the service cable or similar work. Mostly urban. Phases at 120 degrees. Vl/Vp=sqrt(3)
Split phase (230-0-230) - found where there is only single-phase HV, mostly rural. Would require new HV line and transformer to upgrade to 3-phase. Phases at 180 degrees. Vl/Vp=2
Genuine 2-phase power - went out with the ark, but was a competitive system in the early days of AC. If you find this in the UK, call me. I want to document it and maybe pinch the Scott transformer that's feeding it. Phases at 90 degrees. Vl/Vp=sqrt(2)