An absolute phrase has a subject, but not an action verb, so it cannot stand alone as a complete sentence. It modifies the whole sentence, not just a noun.
Examples:
Their heads hanging down, the whole group apologized.
Picnic basket in hand, she set off for her date.
His tail between his legs, the dog walked out of the door.
The entire team, their uniform muddy and stained, shouted for joy.
Points to remember while using phrase:
Phrases are a part of the sentence and cannot stand alone.
They do not give complete meaning if taken out of a context.