The rebus principle is a bit more general: it's when a logogram for something is extended to represent the phonemes making up the name of that thing in other contexts. For example, the Sumerian word for "mouth" was pronounced ka; when Sumerian scribes started using the "mouth" logogram to mean the sound
/ka/ in other contexts that had nothing to do with mouths (e.g. to spell out case markers), that was the rebus principle in action. A modern example would be using the symbol "2" as an abbreviation for "to" or "too".
The acrophonic principle (or acrophony) is related, but involves repurposing a logogram for specifically the first sound of its name. When a Proto-Sinaitic scribe took a hieroglyph of a house (Egyptian pr, Semitic bayt) and used it for the sound
/b/, that was acrophony in action.
The term "acrophony" is also sometimes used in the other direction, for naming (inherited or invented) alphabet letters after words. For example, the NATO spelling alphabet (alpha, bravo, charlie…) would be considered acrophonic by this definition.