There should be an option in Tools > Options > Editor > Formatting > PHP > Blank Lines that controls the number of blank lines between case and default blocks within switch statements.

So this:

switch($var) {
  case 0:
    echo 'foo';


  case 1:
    echo 'bar';
  default:
    echo 'baz';
}

with having the formatter set to 1 line between cases gets formatted as:

switch($var) {
  case 0:
    echo 'foo';

  case 1:
    echo 'bar';

  default:
    echo 'baz';
}

Sebastian