Your design is proper only you have to do is you will have to replace your button part in your markup code with this
<asp:Button ID="Button1" runat="server" Text="Submit" OnClick="OnSubmitClick" />
Now you will have to write this code in default.cs
Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Public Partial Class _Default
Inherits System.Web.UI.Page
Protected Sub Page_Load(sender As Object, e As EventArgs)
End Sub
Protected Sub OnSubmitClick(sender As Object, e As EventArgs)
Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
Dim connection As New SqlConnection()
connection.ConnectionString = conString
connection.Open()
Dim command As New SqlCommand("INSERT INTO [users] ([name], [email], [phone]) VALUES (@n,@e,@p)", connection)
command.Parameters.Add(New SqlParameter("@n", TextBox1.Text))
command.Parameters.Add(New SqlParameter("@e", TextBox2.Text))
command.Parameters.Add(New SqlParameter("@p", TextBox3.Text))
command.ExecuteNonQuery()
connection.Close()
End Sub
End Class
and check whether it works