Halliday & Matthiessen (2014: 437n):
It is important to maintain the terminological distinction between group and phrase, which is lost if a nominal group is referred to as a ‘noun phrase’. Although group and phrase are both of intermediate rank as constituents, they have arrived there from different ends: a group is a bloated word, whereas a phrase is a shrunken clause. In Bloomfield’s (1933: 194–195) terms, groups are endocentric constructions whereas phrases are exocentric ones.