Leaving aside "interjections", we recognise eight (8) word categories (parts of speech). Six (6) of them can function as the head of corresponding phrases: the other two can’t. The very small coordinator and subordinator classes do not function as head but serve as markers of coordination and subordination: there is no such thing as 'coordinator phrases' or 'subordinator phrases'.
[1] Noun (NP) “this clear case of dedication to duty”
[2] Verb (VP) “saw something in there”
[3] Adjective (AdjP) “very eager for further news”
[4] Determinative (DP) “almost every”
[5] Adverb (AdvP) “quite separately from this issue”
[6] Preposition (PP) “right out of the area”
[7] Coordinator (no phrasal category)
[8] Subordinator (no phrasal category)
Note: pronouns are not treated as a distinct part of speech, but as a subclass of noun.