TextBox txt = new TextBox();
txt.Id ="txt1";
txt.Text="something;
PlaceHolder1.Controls.Add( txt); // adding controls dynamically

foreach ( Control ctrl in PlaceHolder1.Controls )
{
 if ( ctrl is TextBox )
  {
   TextBox txt = (TextBox)ctrl;
   //accessing values of dynamically created controls
   string textBoxVal = txt.Text; 
  }
}