使用表单更新已完成的数据库条目？

I have a form that has drop down boxes in it as well as text fields and a checkbox. What I am trying to do is make it so that when a user goes on this page and the address bar displays /updatephoneform.php?id=1, the form displays the information for id1 (PhoneID in my database) and so it can be edited and updated. How would I modify my form to do this? The variables and form are below:I have a form that has drop down boxes in it as