Can you mock how you intend to visualize this? This could be either very easy, or very difficult, but it depends on what you are trying to do.
The end result is the data will be copied and pasted into a spreadsheet. There just needs to be one row for each unique id.
If that is the case, I might suggest doing in a spreadsheet instead of Tableau, or in an application.
Tableau can't really do string concatenations from records in multiple rows, you could, but it wouldn't be efficient or scale.
You could do this...
1. Put Name on Row Shelf
2. Put Phone Number on the Detail Marks Card
3. Create a calculated field => INDEX()
4. Place that calculated field onto the Columns Shelf
4A. Set the calculated field to Compute using Phone Number, Restarting every Name
It won't be perfect, but it would allow your user to copy and paste it.