Anndroid App + PHP + MySQL

I'm doing an app for Android that makes a login to a server in MySQL , it must first go through a php file where it connects to the server and picks up the user and password of who is going to login. I made the php file that connects to the server (I'm going through steps that I'm new to this) so far, the browser returns that the server is connected.

<?php 
$conn = new mysqli("127.0.0.1:3306", "root", "abc123.", "clients");
if($conn->connect_errno>0){
die('Imposible conectar['.$conn->connect_errno.']');
}else{
echo 'Conectado';
} 
?>

In the Android app I added the php file of connected or not connected, but when I start the app on the physical mobile I jump to the catch of the class httpHandler, I guess it is not able to read the php. MainActivity :

public class WindowPrincipalLogin extends AppCompatActivity {
private TextView status;
private String txt;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.windowgraphic_pl);
    StrictMode.ThreadPolicy policy = new 
    StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode.setThreadPolicy(policy);

    httpHandler han = new httpHandler();
    txt = han.post("http://localhost/prueba/conn.php");
    status.setText(txt);

Class that I call from the Main that executes the thread:

public class httpHandler {

public String post(String posturl){
    try {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(posturl);
        HttpResponse resp = httpclient.execute(httppost);
        HttpEntity ent = resp.getEntity();
        String text = EntityUtils.toString(ent);
        return text;

    } catch (Exception e) {
        return "Fallo en la conexión al servidor"+e.getMessage();
    }
}