These two components are optional. In their absence, R1 becomes a short and C1 is left open. While there should be no reason to leave out C1, R1 can decrease the voltage of the phantom power supply, possibly compromising the performance of some microphones. You can calculate this voltage drop using Ohm's Law to see if it will be harmful. For example, if R1 is 1kΩ and the mic is drawing 5mA of current, then there's a loss of 5VDC. 48 - 5V = 43V, which shouldn't be a problem for most mics, but still something to consider.