  The amplitude-phase formulation of the Schr\"{o}dinger equation is
investigated within the context of uncoupled Ermakov systems, whereby the
amplitude function is given by the auxiliary nonlinear equation. The classical
limit of the amplitude and phase functions is analyzed by setting up a
semiclassical Ermakov system. In this limit, it is shown that classical
quantities, such as the classical probability amplitude and the reduced action,
are obtained only when the semiclassical amplitude and the accumulated phase
are non-oscillating functions respectively of the space and energy variables.
Conversely, among the infinitely many arbitrary exact quantum amplitude and
phase functions corresponding to a given wavefunction, only the non-oscillating
ones yield classical quantities in the limit $\hbar \to 0$.
