in linguistics, especially within generative grammar, phi features (denoted with the greek letter φ 'phi') are the semantic features of person, number, gender, and case, as encoded in pronominal agreement with nouns and pronouns (the latter are said to consist only of phi-features, containing no lexical head). several other features are included in the set of phi-features, such as the categorical features ±n (nominal) and ±v (verbal), which can be used to describe lexical categories and case features.