code: def open_phbst(self):
          
          from abipy.dfpt.phonons import PhbstFile
          phbst_path = os.path.join(self.workdir, "run.abo_PHBST.nc")
          if not phbst_path:
              if self.status == self.S_OK:
                  logger.critical("%s reached S_OK but didn't produce a PHBST file in %s" % (self, self.outdir))
              return None
  
          try:
              return PhbstFile(phbst_path)
          except Exception as exc:
              logger.critical("Exception while reading GSR file at %s:\n%s" % (phbst_path, str(exc)))
              return None
docs: Open PHBST file produced by Anaddb and returns :class:`PhbstFile` object.