We use gravity and topography data to study crust and mantle structure in Phoebe Regio and Devana Chasma on Venus. We find that Phoebe is a region of thickened crust and hotter than normal mantle. These results are inconsistent with a cold, downwelling model and may support a mantle plume origin for Phoebe. However, the pattern of thermal anomalies is unusual, with temperature maxima on the periphery of the highland rather than in its center. This may reflect development of thermal boundary layer instabilities as the plume head interacts with the lithosphere. The hot mantle anomaly beneath Devana Chasma is discontinuous near latitude 10 North, coinciding with a 600 km offset in the rift zone trend. Devana should be regarded as two separate rifts, one propagating south from Beta Regio and the other propagating north from Phoebe Regio. Our results support the view that Venus remains a geologically active world.