  We simulate the dynamics of Au+Au collisions at the Relativistic Heavy Ion
Collider (RHIC) with a hybrid model that treats the dense early quark-gluon
plasma (QGP) stage macroscopically as an ideal fluid, but models the dilute
late hadron resonance gas (HG) microscopically using a hadronic cascade. By
comparing with a pure hydrodynamic approach we identify effects of hadronic
viscosity on the transverse momentum spectra and differential elliptic flow
v_2(p_T). We investigate the dynamical origins of the observed mass-ordering of
v_2(p_T) for identified hadrons, focusing on dissipative effects during the
late hadronic stage. We find that, at RHIC energies, much of the finally
observed mass-splitting is generated during the hadronic stage, due to build-up
of additional radial flow. The phi meson, having a small interaction cross
section, does not fully participate in this additional flow. As a result, it
violates the mass-ordering pattern for v_2(p_T) that is observed for other
hadron species. We also show that the early decoupling of the phi meson from
the hadronic rescattering dynamics leads to interesting and unambiguous
features in the p_T-dependence of the nuclear suppression factor R_AA and of
the phi/p ratio.
