An individual sound cluster, properly articulated, is referred to as a word in adults, but to very young children it can be much more. Expressed in various ways, it can communicate emotion or actions/activities. Young children may only have enough short term memory to articulate one sound cluster--but intend to communicate a great deal with that cluster. As they learn to "clump" multiple clusters, they expand communication into phrases and sentences--groupings of sound clusters become expansions of single words and begin to take on grammatical structure: a noun>verb>object action sequence.
Humans are capable of communicating with each other without any spoken language--especially if they are living together--using gestures, facial expressions, and touch. That never goes away.
The challenge for the alphabet maker is to design a vehicle that incorporates the communication possibilities of spoken language and non spoken communication as much as possible--knowing much will be left out.