create a function which accepts two numbers and a symbol to indicate if the user wants to add, substract, multiply, or divide. Include the call to the function in a try/catch structure to capture any attempt to divide by zero

<?php
function add(int $add1, int $add2){
    $result = $add1 + $add2;
    return $result;
}
function subtract(int $subtract1, int $subtract2){
    $result1 = $subtract1 - $subtract2;
    return $result1;
}
function multiply(int $multiply1, int $multiply2){
    $result2 = $multiply1 * $multiply2;
    return $result2;
}
function divide(int $divide1, int $divide2){
    $result3 = $divide1 % $divide2;
    return $result3;
}


$a = "divide";
switch ($a) {
    case "add":
        echo add(12,12);
    break;

    case "subtract":
        echo subtract(12,3);
    break;

    case "multiply":
        echo multiply(12,12);
    break;

    case "divide":
        echo divide(12,2);
    break;

    default:
        echo "String was not found";
    break;
}

bertrc
$result3 = $divide1 % $divide2;

The division operator is /, you used the modulus operator %.

      And because I'm bored, a bit of a modification to allow using floats as well, directly returning the operation instead of storing it in a variable, handling the divide by 0 potential, and leveraging the ability to reference a function via a variable to allow more streamlined testing (IMO):

      function add(int|float $add1, int|float $add2){
  return $add1 + $add2;
}
function subtract(int|float $subtract1, int|float $subtract2){
  return $subtract1 - $subtract2;
}
function multiply(int|float $multiply1, int|float $multiply2){
  return $multiply1 * $multiply2;
}
function divide(int|float $divide1, int|float $divide2){
  if($divide2 == 0) { throw new Exception("Divide by zero not allowed"); }
  return $divide1 / $divide2;
}

$tests = [[1, 2], [4.5, 3.2], [0, 99.999], [-99, 0.0]];
$ops = ['add', 'subtract', 'multiply', 'divide'];
try {
  foreach($tests as [$a, $b]) {
    foreach($ops as $op) {
      echo "$a $op $b = " . $op($a, $b) . "\n";
    }
  }
} catch(Exception $e) {
  echo $e->getMessage()."\n";
}

/* Output:

1 add 2 = 3
1 subtract 2 = -1
1 multiply 2 = 2
1 divide 2 = 0.5
4.5 add 3.2 = 7.7
4.5 subtract 3.2 = 1.3
4.5 multiply 3.2 = 14.4
4.5 divide 3.2 = 1.40625
0 add 99.999 = 99.999
0 subtract 99.999 = -99.999
0 multiply 99.999 = 0
0 divide 99.999 = 0
-99 add 0 = -99
-99 subtract 0 = -99
-99 multiply 0 = -0
Divide by zero not allowed
*/

      All that being said, if this is some sort of assignment that specifically wants you to "create a function which accepts two numbers and a symbol", I guess this does not answer that, as you have created 4 separate functions. In that case, you probably want that switch (or something similar) within the target function, which would accept the operation as a third parameter, something like:

      function arithmetic(int|float $a, int|float $b, string $operation): int|float {
  switch(strtolower($operation)) {
    case 'add':
      return $a + $b;
      break;
    case 'subtract':
      return $a - $b;
      break;
    case 'multiply':
      return $a * $b;
      break;
    case 'divide':
      if($b == 0) { throw new Exception("Division by zero not allowed"); }
      return $a / $b;
      break;
    default:
      throw new Exception("Invalid operation '$operation'");
  }
}

$tests = [[1, 2], [4.5, 3.2], [0,99.999], [-99, 0.0], [5, 10]];
$ops = ['add', 'subtract', 'multiply', 'divide'];
try {
  foreach($tests as [$a, $b]) {
    foreach($ops as $op) {
      echo "$a $op $b = " . arithmetic($a, $b, $op) . "\n";
    }
  }
} catch(Exception $e) {
  echo $e->getMessage()."\n";
}
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