phonetic determinative

noun1

1. •
   a type of hieroglyph that functions similarly to a phonogram, representing a series of consonants, but is unable to function autonomously and must follow other phonograms that together represent the same consonants

   • It is difficult to know whether the boat hieroglyph was merely intended as an ideogram, or as a phonetic determinative for the verb ḫd, ‘to fare downstream’. — 2012