The nucleation and the structural and optical properties of InP nanowires (NWs) grown on Si(111) by molecular beam epitaxy using the vapor-liquid-solid method with gold-indium droplets as catalyst are investigated as a function of the temperature of the formation of the catalyst droplets and of the NW growth time. It is highlighted a complex behavior of the gold-indium catalyst droplets depending on the temperature. It is then shown than an InP pyramid-like pedestal is formed prior to the NW growth. When the temperature of formation of the catalyst droplets is lower than 550 degrees C, almost only vertically standing pure wurtzite InP NWs are grown on Si(111).