This chart is from Tal Tovy, The Theoretical Aspect of Targeted Killings: The Phoenix Program as a Case Study (2009; .pdf link at bottom of abstract), summarizing neutralization of VCI (Viet Cong Infrastructure):

Phoenix Stats 1968-1972.jpg

The footnotes show 1972 as a partial year; and Moyer's book as the source for the chart:

66 Until July 1972, when the Phoenix Program ended as part of the process of evacuation of the American forces from South Vietnam.

67 Source: Mark Moyer, Phoenix and the Birds of Prey – The CIA's Secret Campaign to Destroy the Viet Cong, p. 236.
There are a number of online articles that get into Vietnam War detentions arising from Pacification in general and Phoenix in particular; but those tend to be more qualitative than quantitative.

I'll stop now and you can tell us what type of historical data would be useful.

Regards

Mike