Sensory Short-term memory enables us to recognize phonemes.
Short-Term Memory, is the ability to hold on to the signal for short periods of time--from milliseconds to hours. It is not, however, a single process but a group of sub sub processes: Sensory, Perceptual and Wrote Memory.
The first, Sensory short-term memory, pertains more to the action of the transducer. In many respects it is the counter part of after imagery in the visual but with a different purpose.
Sensory short term memory holds the image from the transducer long enough for us to recognize is structure.
Without the after glow on a radar screen, for example, patterns would be difficult to discern. Sensory short-term memory performs the same purpose. It enables us to recognize sounds patterns, like phonemes.