$value = 0;
switch($value) {
      case ( $value <= 25 ):
            $CompScore = 'low';
            break;
      case ($value > 25 && $value <= 50 ):
            $CompScore = 'fair';
            break;
      case ($value > 50 && $value <= 75 ):
            $CompScore = 'good';
            break;
      case ($value >75 ):
            $CompScore = 'excellent';
            break;
      default:
            $CompScore = 'low';
            break;
}

echo $CompScore;

(0 == false)    // true
(0 === false)   // false
(1 == false)    // false
(1 === false)   // false
(1 == true)     // true
(1 === true)    // false
(true === true) // true

switch(true) {
       case ($value <= 25):                 // true
             $CompScore = 'low';
             break;
       case ($value > 25 && $value <= 50 ): // false
             $CompScore = 'fair';
             break;
       case ($value > 50 && $value <= 75 ): // false
             $CompScore = 'good';
             break;
       case ($value >75 ):                  // false
             $CompScore = 'excellent';
             break;
       default:                             // if you removed the first case
             $CompScore = 'low';            // this default case would be used
             break;
 }

// from excellent to low
if ($value > 75) {
  $CompScore = 'excellent';
} else if ($value > 50) {
  $CompScore = 'good';
} else if ($value > 25) {
  $CompScore = 'fair';
} else {
  $CompScore = 'low';
}

$value = 0;
Switch ($value){
    case ($value < 25):
        ....

}

($value<25) == $value.
=> true == 0

$lookup = [
    1 => 'low',
    2 => 'fair',
    3 => 'good',
    4 => 'excellent'
];

for ($i = -1; $i <= 101; ++$i) {
    echo "n$i : " , $lookup[ceil($i / 25)] ?? $lookup[1];
}