Which phrase element identifies an abbreviated form of a term?

The choice that identifies an abbreviated form of a term is "ABBR." This HTML tag is specifically designed to denote abbreviations, providing assistance to users and assistive technologies by defining the long form of the abbreviated term. When appropriately used, it increases the accessibility of the document, allowing screen readers to convey the full meaning of the abbreviation to users.

In contrast, other options do not serve the same purpose: "DFN" is used to specify a definition of a term, "ACRONYM" is a specific type of abbreviation that forms a word from the initial letters of a series of words, and "SAMP" is utilized for indicating sample output from a program or similar content, none of which directly addresses the need for marking up standard abbreviations in HTML. Thus, "ABBR" is the accurate choice for identifying an abbreviated form of a term.