  Under the assumption that the $2\leftrightarrow 3$ symmetry is broken only
through phases, we give a systematical investigation of possible lepton mass
matrix forms without referring to the explicit parameter values. The two types
of the $2\leftrightarrow 3$ symmetry are investigated: one is that the left-
and right-handed fields $(f_L, f_R)$ obey the symmetry, and another one is that
only $f_L$ obeys the symmetry. In latter case, in spite of no $2\leftrightarrow
3$ symmetry in the Majorana mass matrix $M_R$ for $\nu_R$, the neutrino seesaw
mass matrix still obey the $2\leftrightarrow 3$ symmetry. Possible
phenomenologies are discussed.
