  A spherically symmetric evolution model of self-gravitating matter with the
equation of state P=wE (where w=const<-1) is considered. The equations of the
model are written in the frame of reference comoving with matter. A criterion
for the existence and formation of a horizon is defined. Part of the Einstein
equations is integrated analytically. The initial conditions and the
constraints imposed on these conditions in the presence of a horizon are
determined. For small |1+w| an analytic solution to spherically symmetric
time-dependent Einstein equations is obtained. Conditions are determined under
which the dynamics of matter changes from collapse to expansion. Characteristic
times of the evolution of the system are evaluated. It is proved that the
accretion of phantom matter (for w<-1) onto a black hole leads to the decreases
of the horizon radius of the black hole (i.e., the black hole is "dissolved").
