Never heard of a Chevy or GM cam referred to as "phase 3"? Hope somebody has, so I'll learn something. I have a copy of Chevy's factory hi performance catalog from the 70's, and don't see a reference in it to that name.
I've been pondering this a bit, and wondered if the terminology might be referring to the last of the high performance versions of the 350 engine? (370 hp LT1) Or perhaps the biggest HP version of the 327 engine? (375 hp) Both engines had 300hp, 350hp, and the top dog a 375hp 327, or the LT1 370hp 350 engine. Wondering if the reference of "phase 3" might be either the 375 hp 327 cam, or the 370 hp 350 cam? Just guessing here.
I remember seeing a reference to Phase III in a casting number identification chart I came across on-line some time ago, referring to 350 heads 96 and up :
12480034 2.02/1.60 Bowtie Phase III 64cc Angle plug 184 cc intake runner. Don't know if this helps or not. I can't remember ever hearing the Duntov 30/30 called phase III.... but then what was the original question?