  We propose a method of describing a phase transition in a cell fluid model
with pair interaction potential that includes repulsive and attractive parts.
An exact representation of the grand partition function of this model is
obtained in the collective variables set. The behavior of the system at
temperatures below and above the critical one is explored in the approximation
of a mean-field type. An explicit analytic form of the equation of state which
is applicable in a wide range of temperatures is derived, taking into account
an equation between chemical potential and density. The coexistence curve, the
surface of the equation of state and the phase diagram of the cell Morse fluid
are plotted.
