The standard way to accept multiple case values (in all C-like languages, including PHP) is to put multiple case labels. It's not quite as succinct as your example, but it does fulfill the purpose of allowing you to only write the handlers once:

switch ($color) {
   case "blue":
   case "green":
   case "aqua":
      echo $color . " is a cool color.";
      break;
   case "red": case "orange": case "brown":
      echo $color . " is a warm color.";
      break;
}

Adding { } around those sections is actually already valid syntax, though in PHP it does nothing because PHP doesn't have block scope (https://en.wikipedia.org/wiki/Scope_%28computer_science%29#Block_scope_within_a_function). In some similar languages, that syntax delimits a scope but doesn't imply a "break;", so PHP could only add that new logic if it's willing to confuse people. It would also break backwards compatibility with any odd code that already has extra { } in its switch handlers.

Several other languages do support fancier rules in their switch statements, though. One variant of the B language (B being the language which first devised the current syntax for the switch statement) allowed ranges such as "case 1 :: 10" and comparisons such as "case >= 5". Most BASICs allow ranges ("CASE 1 TO 10"), comparisons ("CASE IS < 5"), and comma-separated values ("CASE 2, 4, 6"). Ruby allows comma separated values ("when 2, 4, 6") and ranges ("when 1..10").

It would be useful if PHP supported some of those features.

Or... you could just use an if() ;)

As said in a comment:

switch ($color) {
   case "blue":
   case "green":
   case "aqua":
      /* ...*/
}

Exists. As a case statement allows arbitrary expressions linking options without extra case would be painful. We won't change the language there.

.