  The issue of non-Gaussianity is not only related to distinguishing the
theories of the origin of primordial fluctuations, but also crucial for the
determination of cosmological parameters in the framework of inflation
paradigm. We present an advenced method for testing non-Gaussianity on the
whole-sky CMB anisotropies. This method is based on the Kuiper's statistic to
probe the two-dimensional uniformity on a periodic mapping square associating
phases: return mapping of phases of the derived CMB (similar to auto
correlation) and cross correlations between phases of the derived CMB and
foregrounds. Since phases reflect morphology, detection of cross correlation of
phases signifies the contamination of foreground signals in the derived CMB
map. The advantage of this method is that one can cross check the auto and
cross correlation of phases of the derived CMB and foregrounds, and mark off
those multipoles in which the non-Gaussianity results from the foreground
contaminations. We apply this statistic on the derived signals from the 1-year
WMAP data. The auto-correlations of phases from the ILC map shows the
significance above 95% CL against the random phase hypothesis on 17 spherical
harmonic multipoles, among which some have pronounced cross correlations with
the foreground maps. We conclude that most of the non-Gaussianity found in the
derived CMB maps are from foreground contaminations, except, among others, l=6.
With this method we are better equipped to approach the issue of
non-Gaussianity of primordial origin for the upcoming PLANCK mission.
