Find smallest prime number in array

Question

How can I find the smallest prime number in given array? In my given array, how can I return the 7? I used the array sort method. Please help me. Thanks in advance!

<?php
  $array = array(7, 4, 11, 6, 13, 11, 17, 8, 10, 13, 7);
  sort($array);

  $isPrime = 0;
  $count = 0;
  $lowestNumber = null;

  function isJeffian($num) {
      if($num < 2) { 
          return 0;
      }

      for($i = 2; $i <= $num / 2; $i++) {
          if ($num % $i == 0) {
           return 0;
          }
      }

      return 1;

  }

  for($i = 0; $i < sizeof($array); $i++) {
      $isPrime = isJeffian($array[$i]);
      if($lowestNumber == null) {
        $lowestNumber = $isPrime;
      }

      if($isPrime == 1) {
          $count++;
      }
  }
  

  echo "Count of number of primes in array : " . $count . "<br/>";
  echo "Smallest Prime Number: " . $lowestNumber;

?>