Final answer:
The claim about possessive phrases being diagrammed the same as single-word possessives is false. Possessive phrases must be diagrammed to reflect their more complex structure.
Step-by-step explanation:
The statement about possessive phrases being diagrammed in the exact same way as single-word possessives is false. When diagramming possessive phrases, which are longer and involve multiple words, they must be treated differently than single-word possessives.
For example, when diagramming the possessive phrase 'the mayor of the city's decision,' we approach it differently than the simple possessive 'the mayor's decision.' Diagramming takes into account the entire phrase, showing the relationship between 'the mayor of the city' and 'decision' through a possessive use indicated by an apostrophe.