dependencies{
              compile 'com.squareup.okhttp:okhttp:2.0.0'
}

btnRegistration.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                try {

                    String UserName = etUserName.getText().toString();
                    String Password = etPassword.getText().toString();
                    String DOB = etDob.getText().toString();
                    String Phone = etPhone.getText().toString();


                    String inserturl = "http://10.0.2.2/Project/Registration.php?insert&username="+UserName+"&password="+Password
                            +"&dob="+DOB+"phone="+Phone;

                    JSONObject jsonObject = new JSONParser().SelectData(inserturl);

                    if (jsonObject != null)
                    {
                        Toast.makeText(MainActivity.this, jsonObject.toString(), Toast.LENGTH_SHORT).show();

                    }


                }catch (Exception ex){

                    Log.i("Error",ex.toString());
                }


            }

        });

public class JSONParser {


    public JSONObject SelectData(String url){

        try {

            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder().url(url).build();
            Response response = client.newCall(request).execute();
            String data = response.body().string();
            JSONObject jsonObject = new JSONObject(data);
            return jsonObject;


        }catch(Exception ex){


            return  null;

        }
    }
}

<?php

include "Mysql.php";
$username = $_GET['user'];
$password = $_GET['pass'];
$dob =date("Y-m-d" ,strtotime($_GET['dob']));
$phone = $_GET['phone'];

$sql_query = "insert into registration(username,password,dob,phoneno) values('$username','$password','$dob','$phone')";

if(mysqli_query($conn,$sql_query))
{
    echo"<h3>Data Insertion Success...</h3>";
}else{
    echo "Data Insertion error..".mysqli_error($conn);
}

?>