V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

PHIGS
       Programmer's Hierarchical Interactive Graphics System


The Free On-line Dictionary of Computing (30 December 2018):

Programmers Hierarchical Interactive Graphics System
PHIGS

   (PHIGS) An ANSI/ISO standard.  Worked on by the
   ISO/IEC group JTC1/SC24.

   [More detail?]

   (1995-01-04)