System.NullReferenceException: Object reference not set to an instance of an object. in placeholder

Question

I am creating a form from code behind and in my aspx I place a placeholder to create a design but I am not able to retrieve any input values even if I enter an input into the textboxes.

The user data should insert the entered values into the database. I was prompted as null even when I added a default value into the field.

Only the UI appeared but none of the fields are able to retrieve a value from user's input.

protected void Page_Load(object sender, EventArgs e)
    {

        //Get the values from TourPackageDetails.aspx
        int rPackageId = Convert.ToInt16(Request.QueryString["packageId"]);
        int tbCapacity = Convert.ToInt16(Request.QueryString["tbCapacity"]);

        phTravellerForm.Controls.Add(new LiteralControl("<h3>"));
        Label lblTraveller = new Label();
        lblTraveller.Text = "Traveller ";
        phTravellerForm.Controls.Add(lblTraveller);
        phTravellerForm.Controls.Add(new LiteralControl("</h3>"));

        /** Start of  Traveller's name **/
        Label lblName = new Label();
        lblName.Text = "Name: ";
        phTravellerForm.Controls.Add(lblName);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));

        TextBox tbName = new TextBox();
        tbName.Text = "";
        phTravellerForm.Controls.Add(tbName);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));
        /** End of  Traveller's name **/

        /** Start of  Traveller's Contact **/
        Label lblContact = new Label();
        lblContact.Text = "Contact No: ";
        phTravellerForm.Controls.Add(lblContact);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));

        TextBox tbContact = new TextBox();
        tbContact.Text = "";
        phTravellerForm.Controls.Add(tbContact);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));
        /** End of  Traveller's Contact **/

        /** Start of  Traveller's nationality **/
        Label lblNationality = new Label();
        lblNationality.Text = "Nationality: ";
        phTravellerForm.Controls.Add(lblNationality);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));

        TextBox tbNationality = new TextBox();
        tbNationality.Text = "";
        phTravellerForm.Controls.Add(tbNationality);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));
        /** End of  Traveller's nationality **/

        /** Start of passport number **/
        Label lblPassport = new Label();
        lblPassport.Text = "Passport Number: ";
        phTravellerForm.Controls.Add(lblPassport);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));

        TextBox tbPassport = new TextBox();
        tbPassport.Text = "";
        phTravellerForm.Controls.Add(tbPassport);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));
        /** End of passport number **/

        /** Start of passport expiry date **/
        Label lblPassportExpiry = new Label();
        lblPassportExpiry.Text = "Passport Expiry Date: ";
        phTravellerForm.Controls.Add(lblPassportExpiry);

        phTravellerForm.Controls.Add(new LiteralControl("<br />"));

        //Passport expiry date

        TextBox tbDOB = new TextBox();
        tbDOB.Text = "DD/MM/YY";
        phTravellerForm.Controls.Add(tbDOB);
        /**
      tbDOB.Text = this.EditableField.TextValue;
      tbDOB.TextChanged += new EventHandler(tbDOB_OnTextChanged);

      CalendarExtender calExender = new CalendarExtender();
      //calExender.PopupButtonID = "Image1";
      calExender.TargetControlID = tbDOB.ID;
      phTravellerForm.Controls.Add(calExender); **/

        /** End of passport expiry date **/
    }

 protected void btnNext_Click(object sender, EventArgs e)
    {
        TravellerDAL travellerDAL = new TravellerDAL();
        Traveller myTraveller = new Traveller();

        TextBox tbName = phTravellerForm.FindControl("tbName") as TextBox;
        myTraveller.TravellerName = tbName.Text;

        TextBox tbPassport = phTravellerForm.FindControl("tbPassport") as TextBox;
        myTraveller.PassportNumber = tbPassport.Text;
        /**
        CalendarExtender tbPassportExpiry = phTravellerForm.FindControl("tbPassportExpiry") as CalendarExtender;
        myTraveller.PassportExpiryDate = tbPassportExpiry.ToString();
         **/
        TextBox tbNationality = phTravellerForm.FindControl("tbNationality") as TextBox;
        myTraveller.Nationality = tbNationality.Text;
        TextBox tbContact = phTravellerForm.FindControl("tbContact") as TextBox;
        myTraveller.ContactNo = tbContact.Text;

        bool addSuccess = travellerDAL.addTravellerInfo(myTraveller);
        if (addSuccess)
        {
            //No need to bind just saw error messages will do.
            lblAddBookingStatus.Text = "Booking success";
            Response.Redirect("~/TravellerModule/ViewBookingSummary.aspx");
        }
        else
        {
            lblAddBookingStatus.Text = "Oh no! Unable to book please check your entries.";
        }
    }