webform .php read, update and write .xml

I do not know too much regarding the correct method to approach this so please excuse my ignorance on the subject but I require the following: A .php web form to read, update and write to a .xml file (please see the .xml file attached). The form should be dynamic. The .xml consists of numbers delimited by a , . The amount of numbers is unrestricted and could by one or many. Basically I need a web form that will read these and show them. Each number should be able to be changed. Additional numbers should be able to to added and shown in the form dynamically. Equally these should be able to be deleted. IF adding additional numbers or deleting numbers it will always be at the end of the sequence. I hope that makes sense please ask if you require any additional information.