Hi,
PHR is to report the remaining power that UE has. say e.g UE can send data with the maximum power of 21dB, But ENB is asking to send at 18dB (not actually asking , it is configured value by some parameters ), so UE will send 3dB as PHR to saying that UE can increase its UL power level. If increase UL power level then UL data reception will be effective in some case.