Create a Tip Calculator web application using HTML$,$ CSS and PHP$.$ Your application should display an attractively styled form that prompts the user to enter a bill amount in a text field. The form should allow the user to select a radio button associated with a tip percentage. All fields in the form should be required.

When the form is submitted, PHP should be used to create a page that calculates and displays the original bill amount entered, the tip percentage selected, the tip amount, and the combined total of the bill amount and tip amount. $($Note: you may find the number$\_$format$()$ PHP function useful in displaying your output$).$