Efficacy of high power light emitting diodes (LEDs) strongly depends on their thermal management. Heat generated due to non-radiative recombination of carriers in LED active region and due to Stokes losses in phosphor material leads to temperature rise in the device interior and in the phosphor containing silicone layer (PCSL). High temperature in the PCSL influences its thermal quenching behavior and changes luminescence decay time. To achieve high LED efficacy, proper thermal control of PCSL is of the great importance. In this study, we build a thermal model of the LED with PCSL and perform numerical simulations to analyze the heat distribution in the layer. Numerical analysis shows that temperature of PCSL can reach 85 °C and more. At least 30 % temperature drop is demonstrated due to the thickness variation of silicone layer.