The phrase all together (two words) refers to people or things gathered in one place or all acting together.
The adverb altogether (one word) means entirely, wholly, or in all.
- “They came from all parts of Peru. They had never seen each other before but they were all together now, lined up in front of the cement hulks whose insides they had not yet seen.”
(Mario Vargas Llosa, The Time of the Hero, trans. by Lysander Kemp. Grove Press, 1966)