[Merrick]

Single secondary coil supplying two independent phases. If they aren’t independent phases then they can’t fail independently - as I have I lived through twice.

[GingisK]

If they share a common wire, they are not independent phases. Independent phases each have their own secondary. This single secondary has a center tap, but both sides of that tap have current flowing in the same direction, thus a single phase.

A "phase" is associated with a period of a waveform, and they are each at a different phase in the time period. That is why they are named phases in the first place.

I can provide links if you don't want to look this up.

[GingisK]

Single secondary coil supplying two independent phases.

Take a look at post #60 by fruser1.

[GingisK]

Single phase home wiring