  Recently, the observed equation of state for dark energy appears to favor
values below $-1$. The tendency implies that the nature of dark energy may be
quite different from that of the cosmological constant. In view of the
adjustment on the equation of state keeps decreasing, the introduction of the
phantom energy seems inevitable. By employing observational constraints from
supernovae and from the acoustic scale in which the accuracy of the data has
become extraordinary, we apply a phenomenological scenario to be acquainted
with the evolution of our universe. The demonstration on the constrained
unfolding of the phantom energy shows the model has high consistency with the
current observation.
