Is there a term for coining a phrase for a word that already exists?

You have named textbook cases of the retronym, which AHD defines as

A word or phrase created because an existing term that was once used alone needs to be distinguished from a term referring to a new development, as acoustic guitar in contrast to electric guitar or analog watch in contrast to digital watch.

Language Log and others ascribe the term ca. 1980 to Frank Mankiewicz, a writer and Democratic political strategist who was later head of National Public Radio. You can find a large collection of them at Retronyms.org.

For a related phenomenon, see Word that means “outdated name”.