  We show that classicality emerges during quantum phase transitions due to
parametric interactions without coupling to environments. The Wigner functions
are explicitly calculated for the Gaussian vacuum, number, and thermal states
of a free scalar field that describes the spinodal instability regime. The
Wigner functions are sharply peaked around their classical trajectories during
the phase transition and exhibit classical correlation only for unstable long
wavelength modes but retain quantum coherence for short wavelength modes. Thus
classicality emerges from the quantum evolution of phase transitions without a
classical order parameter. We define a quantal ordering parameter that is
linear in the field variable and satisfies the classical field equation.
