"Designating or relating to the classification of organisms on the basis of their observed similarities and differences (often assessed in numerical terms), without reference to functional significance or evolutionary relationships".The term was first used by Cain and Harrison (1960) "[f]ollowing a suggestion made by Mr. H. K. Pusey, we shall refer to the arrangement by overall similarity, based on all available characters without any weighting as phenetic, since it employs all observable characters (including of course genetic data when available)" (Cain and Harrison, 1960: 3).
The OED defines the term phenetics as "phenetic taxonomy or the systematics of phenotypes". It was first used by Ehrlich & Holm (1963) to refer to "[t]he study of relationships of individuals [which] may permit the creation of a 'population phenetics' which will add new dimensions to the study of microevolution" (Ehrlich & Holm, 1963: 240-2).
If the first definition of phenetic is true, then phenetics by definition cannot find evolutionary or phylogenetic relationships, only similarities.
Cain A.J. & Harrison G.A. (1960) Phyletic Weighting. Proceedings of the Zoological Society of London 135: 1–31.
Ehrlich P. & Holm R.W. (1963) Letter to the Editor. Science 139: 240 – 242.