Hi carassius,
Thanks for using Conditional Logic
As your requested, I've created a snippet with comments so you can see and use in your project. Basically, I use a 'post' field to display all customers and create a phone field which store customer phone and a set of phone fields equal to num of customers which has default value inside, when user post data, the visible phone field will replace default phone field. Have fun 🙂
https://pastebin.com/6qC7CJwh