All three used for feedback as expected by eNB from an UE to maximize the throughput with more reliability.
Channels conditions are more frequent to change. So Ue sends feedback to eNB about Ue is absorbing the radio. eNB receives all 3 parameters from UE then it consider all these parameters for next transmission of data.
CQI stands for channel quality indicator, based on received CQI value eNB uses proper modulation and coding rate for transport block.
PMI and RI comes into picture in case MIMO. There is a term "closed loop spatial multiplexing" . PMI is used for that purpose. for 4*4 MIMO there are 16 possible precoding matrix index.
RI is also used for MIMO. LTE UE supports max 2*2 MIMO. So R1 value ranges[1 - 2] based on Transmitter and receiver combination.
Frequency of reporting CQI is highest as compare to PMI/RI.
Even if RI and PMI related to MIMO schemes but both are independent to each other.