Speaking professionally, I would say the phrase counts as "commonly used" and therefore does not fall under plagiarism. The length of the phrase doesn't really matter for plagiarism purposes, so long as the phrase is "unique". Intent of usage and interpretation don't really matter either
That said, the question of plagiarism is, in this case, the wrong question. Since you're considering the work for future publication, copyright is the appropriate concern. But, I would say you're safe there too, under U.S. copyright law at least.
(Clarification: plagiarism = ethical/professional concern and is enforced by employers/academic institutions; copyright = legal concern and is enforced by the federal govt)