PHP will turn an array of characters

explode(',',$arr_string)

// string transfer array 
$ arr_string = 'l, 2,3' ;
 $ ARR = the explode ( ',', $ arr_string );
dump($arr);

// print out the following 
Array (. 3 ) {
  [0] => string(1) "1"
  [1] => string(1) "2"
  [2] => string(1) "3"
}