He says he was in the Marines 72-76. Paris treaty was January 1973. This smells...I hope it is followed up on by someone who knows more.
Here’s some information on Marines in Vietnam from the Marine Corps history of the Vietnam War, in 21 volumes, published by the United States Marine Corps’ History and Museums Division, created from 1968 to 2009:
“On 14 April 1971, III MAF redeployed to Okinawa, and two months later the last ground troops, the 13,000 men of the 3d MEB, flew out from Da Nang.
Although Marine combat units were no longer in Vietnam, Marine advisors remained to assist the South Vietnamese.”
http://www.paperlessarchives.com/vw_marine_corps_official_histo.html
So, it appears that the last Marine Corps forces left Vietnam in June of 1971. Only ones to remain were the advisors and the embassy guards. It seems unlikely that Phillips would have been either an advisor or embassy guard at the age of 17.