With the ESC unplugged from everything, use a multimeter and check the resistance between:
Battery Neg to ESC Phase A: ?Ω
Battery Neg to ESC Phase B: ?Ω
Battery Neg to ESC Phase C: ?Ω
Battery Pos to ESC Phase A: ?Ω
Battery Pos to ESC Phase B: ?Ω
Battery Pos to ESC Phase C: ?Ω