c - Why use double pointer when inserting node to the head (linkedlist)?

int list_insert_head(node **phead, int data){
  node *newnode = malloc(sizeof(node));
  if(newnode == 0)
    return 0; /*memory allocation failed*/
  newnode -> data = data;
  newnode -> next = *phead;
  *phead = newnode; /* what is this?*/
  return 1;
}

So I'm not quite sure why you have to pass in double pointer **phead,
and only use a single pointer *phead inside the function.
I assume you use double pointer b/c you're manipulating actual head, which itself is a single pointer.
Inside the function by the way, if you were going to do this,

*phead = newnode;

why don't you just pass in *phead in the function parameter?

Thank you.