How to know how many phases a BLDC has?
Nearly all BLDC motors have three phases.  Like, more than 99%, as far as I know.  But if it's oddball and has two, then it needs three wires (phase 1, phase 2, and common) or four.  Similarly, an oddball 3-phase BLDC may have six wires (i.e., the manufacturer decided to bring out each phase individually).

The only way to tell for sure is to do some continuity checks, then put it up on an oscilloscope, spin it, and look at what it generates.