  Recent neutrino oscillation experiments suggest that the PMNS matrix in the
lepton sector has a $CP$ violating phase as the CKM matrix in the quark sector.
However, origin of these phases in both matrices are not clarified by now.
Although complex Yukawa couplings could induce these phases, they remain as
free parameters of the model even in that case. If the $CP$ symmetry is
considered to be spontaneously broken, they are expected to be determined by
some physics at a much lower energy scale than the Planck scale. We study such
a possibility in a framework of Pati-Salam type unification. We also discuss
other phenomenological issues in it.
