  An outburst of the accreting X-ray millisecond pulsar SAX J1808.4-3658 in
October-November 2002 was followed by the Rossi X-ray Timing Explorer for more
than a month. We demonstrate how the area covered by the hotspot at the neutron
star surface is decreasing in the course of the outburst together with the
reflection amplitude. These trends are in agreement with the natural scenario,
where the disc inner edge is receding from the neutron star as the mass
accretion rate drops. These findings are further supported by the variations of
the pulse profiles, which clearly show the presence of the secondary maximum at
the late stages of the outburst after October 29. This fact can be interpreted
as the disc receding sufficiently far from the neutron star to open the view of
the lower magnetic pole. In that case, the disc inner radius can be estimated.
Assuming that disc is truncated at the Alfv\'en radius, we constrain the
stellar magnetic moment to \mu=(9\pm5) 10^{25} G cm^3, which corresponds to the
surface field of 10^8 G. On the other hand, using the magnetic moment recently
obtained from the observed pulsar spin-down rate we show that the disc edge has
to be within factor of two of the Alfv\'en radius, putting interesting
constraints on the models of the disc-magnetosphere interaction. We also
demonstrate that the sharp changes in the phase of the fundamental are
intimately related to the variations of the pulse profile, which we associate
with the varying obscuration of the antipodal spot. The pulse profile amplitude
allows us to estimate the colatitude of the hotspot centroid to be 4-10 deg.
