Phase Impenetrability Condition: A constraint on grammatical operations which specifies that the domain/complement of a phase head is impenetrable/inaccessible to an external probe (. to a c-commanding probe which lies outside relevant phase). See § and §. Phi-features/f-features: Person and number features (and, in languages which have grammatical gender, gender features as well). Phonetic representation: See Representation. Phonological features: