<select value="center_name" ng-model="selectedname" ng-options="name.center_name for name in namelist" ng-change="loadcounsellors(selectedname)">
        <option >Please select a name</option>
    </select>

var app=angular.module('myapp',[]);
app.controller('MyCtrl',function($scope,$http,$httpParamSerializer)
{
  $http.get("logintype.php")
  .then(function(response)
{
  $scope.namelist=response.data;

})
$scope.loadcounsellors=function(item){
  alert(item.center_name);
 $http.post("counselorlist.php",$httpParamSerializer({center_name:item.center_name}))

  .then(function(response)
{
  // alert("hello world");
  $scope.counsellor=response.data;
  alert(response.data);

})
}
})

             <h2>Selected: {{counsellor}}</h2>

<?php

require "connection.php";
// $postdata = file_get_contents("php://input");
// $params = json_decode(file_get_contents('php://input'), true);
// $request1 = json_decode($postdata);
// echo $request1;
$center_name = $_POST['center_name'];
echo $center_name;
// $center_name = "Andheri"; //This works fine.
$query = "select distinct(edited_by) from telephonic_enquiry
 where center_name='$center_name'";
$result = mysqli_query($conn, $query);
if (mysqli_num_rows($result)>0 ) {
    $response=array();
    while ($row= mysqli_fetch_array($result)) {
        array_push(
            $response, array (
            'edited_by'=>$row['edited_by'],
            )
        );
    }
    echo json_encode($response);
}
mysqli_close($conn);
?>