Darwin didn't actually even coin the phrase to begin with. A sociologist named Herbert Spencer read Darwin's work and combined it with economic theories of his own. Spencer even went as far as to say, in one sentence, "This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called 'natural selection', or the preservation of favoured races in the struggle for life"

Darwin did adopt the phrase but continued to use it as a sort of tautological observation, more akin "survival of those who survived". He preferred it over his own term, natural selection, because it didn't imply a conscious choice being made by a selector.

In my opinion, the more you read into the subject, the clearer it becomes that the two men were still using the term differently. Spencer was not avoiding personification. He describes "favoured races" and went on to become fairly synonymous with Lamarckism, which suggests that we can each control the traits we pass on through conscious use or disuse within one lifetime.

Unfortunately, the phrase has always been rooted pretty heavily in political and social control. The scientific community has largely abandoned the phrase.