  The phenomenon of the large phase shift of the strongly nonlocal spatial
optical soliton was predicted by Guo et al. within the phenomenological
framework [Q. Guo, et al., Phys. Rev. E 69, 016602 (2004)], but has not been
experimentally confirmed so far. We theoretically and experimentally
investigate the large phase shift of that propagating in the lead glass. It is
verified that the change of the optical power carried by the optical beam about
10 mW around the critical power for the soliton can lead to a {\pi} phase
shift, which would be of its potential in the application of all-optical
switchings.
