After the war the communist said that the Phoenix program was very successful.

The communist insurgency in Vietnam was beaten many times. In Mark Moyars' Triumph Forsaken he notes that in 1959 the Diem regime had reduced the communist forces down to just 6,000 men.

After the north started sending more troops down, they were defeated again in the early '60's. What helped them in 1963 was their infiltration of the Buddhist movement creating what appeared to be a sectarian strife.

The US fell for the ruse and started putting pressure on Diem to make concessions to the Buddhist leaders who kept moving the goal post. State Department people began back a coup against Diem and were assisted in that effort by Ambassador Lodge and some reporters in Vietnam who later received Pulitzer Prizes for their efforts. The coup caused the South Vietnamese to lose momentum in their war against the communist, and President Johnson's weak response to provocations encouraged them to send more troops south.

If you are interested in counterinsurgency warfare, you will want to read Moyar's book. It only goes through 1965, so you will probably have to wait for the next volume to read about the CORDS program from his perspective.