  This paper presents a phase description of chaotic dynamics for the study of
chaotic phase synchronization. A prominent feature of the proposed description
is that it systematically incorporates the dynamics of the non-phase variables
inherent in the system. Taking these non-phase dynamics into account is
essential for capturing the complicated nature of chaotic phase
synchronization, even in a qualitative manner. We numerically verified the
validity of the proposed description in application to the R\"{o}ssler and
Lorenz oscillators, and we found that our method provides an accurate
description of the characteristic distorted shapes of the synchronization
regions for these chaotic oscillators. Furthermore, the proposed description
allows us to systematically identify and describe the origin of this
distortion.
