  We report six stellar occultations by (Saturn IX) Phoebe, an irregular
satellite of Saturn, obtained between mid-2017 and mid-2019. The 2017 July 06
event is the first stellar occultation by an irregular satellite ever observed.
The occultation chords were compared to a 3D shape model of the satellite
obtained from Cassini observations. The rotation period available in the
literature led to a sub-observer point at the moment of the observed
occultations where the chords could not fit the 3D model. A procedure was
developed to identify the correct sub-observer longitude. It allowed us to
obtain the rotation period with improved precision over currently known value
from literature. We show that the difference between the observed and the
predicted sub-observer longitude suggests two possible solutions for the
rotation period. By comparing these values with recently observed rotational
light curves and single-chord stellar occultations, we can identify the best
solution for Phoebe's rotational period as $9.27365 \pm 0.00002$ h. From the
stellar occultations, we also obtained 6 geocentric astrometric positions in
the ICRS as realised by the Gaia-DR2 with uncertainties at the 1-mas level.
