  We perform phase-resolved spectroscopy of the accreting millisecond pulsar,
SAX J1808.4-3658, during the slow-decay phase of the 2002 outburst. Simple
phenomenological fits to RXTE PCA data reveal a pulsation in the iron line at
the spin frequency of the neutron star. However, fitting more complex spectral
models reveals a degeneracy between iron-line pulsations and changes in the
underlying hotspot blackbody temperature with phase. By comparing with the
variations in reflection continuum, which are much weaker than the iron line
variations, we infer that the iron-line is not pulsed. The observed spectral
variations can be explained by variations in blackbody temperature associated
with rotational Doppler shifts at the neutron star surface. By allowing
blackbody temperature to vary in this way, we also find a larger phase-shift
between the pulsations in the Comptonised and blackbody components than has
been seen in previous work. The phase-shift between the pulsation in the
blackbody temperature and normalisation is consistent with a simple model where
the Doppler shift is maximised at the limb of the neutron star, ~90 degrees
prior to maximisation of the hot-spot projected area.
