Phi Meson Propagation and Decay in Hot Hadronic Matter Based on vacuum properties, the phi meson is expected to=20 decay outside the fireball generated in heavy-ion collisions. One-loop thermal effects turn out to be rather small, leaving the spectral function and also the lifetime unchanged. Two-loop effects contribute to collision broadening and, in contrast, are rather significant. We use an in-medium spectral function for the phi to extract a lifetime at finite temperature. The lifetime is shortened sufficiently to allow decay inside the fireball. Dilepton decay channels could be used to probe these collective effects.