i think this is what you are trying to do, but maybe not
if the textbox is like an html textarea, then the numbers would be added like this in the same textarea named "numbers":
800-555-1212
800-555-2323
800-555-3434
each number can be seperated by a new line.. then before you insert the numbers in the database, split them into an array:
$array=split("\n",$numbers);
now you will have each number in a seperate variable named "$array[]" and you can insert them as you normally do into your db.
hope this helps
-mike