  The phase diagram of antiferromagnetic spin-S chain with XY-type anisotropy
and frustrating next-nearest-neighbor interaction is studied in the limit of
large integer S with the help of a field-theoretical approach. It is shown that
the existence of gapless and gapped chiral phases found in recent numerical
studies [M.Kaburagi et al., J. Phys. Soc. Jpn. vol.68, 3185 (1999), T.Hikihara
et al., J. Phys. Soc. Jpn. vol.69, 259 (2000)] is not specific for S=1, but is
rather a generic large-S feature. Estimates for the corresponding transition
boundaries are obtained, and a sketch of the typical phase diagram is
presented. It is also shown that frustration stabilizes the Haldane phase
against the variation of the anisotropy.
