php Create a button to call a function inside a fetch_accoc

Question

I have a web page which is using php code to search and retrieve images matching tags the user enters. It is using mysql to store the image paths and retrieve the images for the user along with image information.

I'm trying to create a button within each retrieved image information to select it for download. This button will update the database table flag field. My problem is that I can't seem to call the function inside the fetch image/image info loop. I've tried one click methods and $_POST calls.

Thanks in advance

function fun(){
              echo "Hello";
          }

   if(isset($_POST['insert'])){
        $message= "The insert function is called.";
        echo "The insert function is called.";
        
    }
    if(isset($_POST['select'])){
        $message="The select function is called.";
    }


$searchTags = $_POST['searchTag'];

$conn = new mysqli($servername,$username,$password,$db);

if ($conn->connect_error) {
    die("Connection Error: ").$conn->connect_error;
}

$sql = "select pic_id, pic_name, pic_description, pic_tags FROM picture where pic_tags like'%$searchTags%'";

$result = $conn->query($sql);

if ($result->num_rows > 0 ){
    while($row = $result->fetch_assoc()) {
        $imgNumber = $row['pic_id'];
        $imgSrc = $row['pic_name'];
        $imgDescription =$row['pic_description'];
        $imgTags = $row['pic_tags'];
        
        echo "<div class='pictureBox'><br>Pic #".$imgNumber." 
        <br><input type='button' value='NEXT' onclick='document.write('<?php 'fun();'?>);       

        <br><input type='submit' name='insert' value='insert'>
        <br>Pic Name: ".$imgSrc."
        <br>Pic Description: ".$imgDescription."
        <br> Pic Tags: ".$imgTags."
        <br><a href='./galleryEditDB.php?picNumber=".$imgNumber."'>Edit</a>
        <br><img src='".$imgSrc."'><br><br></div><br><br>";
        
        echo $value;

    }
} else {
    echo "0 Results";
}

$conn->close();