Always three phases; never three equal phases. van Gennep's own observation was that the emphasis shifts with the kind of passage: separation dominates funerals, incorporation dominates marriages, and the margin swells to fill initiations. The bar under the diagram is that claim, rite by rite.
Liminal, not liminoid. Turner reserved liminal for obligatory rites a whole society requires, which leave the person permanently and publicly changed. For the optional, individual, leisure-time analogues of industrial societies — a festival, a retreat, a gap year — he coined liminoid. The feeling can be very similar. The obligation, and the change in status afterwards, are not.