Matching Users across Platforms

Hi Community and PowerBi Masters,

I am currently working on an analysis for which I try to understand the consumer behavior in detail. 

The corresponding data that I have is (name of table: All_Platforms):

-Order Number

-Order Time

-User Name

-BGR_ALL.Product Name

-BGR_ALL.Category

-Phone Number

-Platform

The ones marked in bold are the ones, which seem to matter for this case.

My goal: understand which consumer has changed between platforms. 

An example: Username Oscaaarrr with Phone number 1925526 has purchased something on Facebook on January first and on Amazon ( 9th February, different user name: YO_Oscar) and a month later on Google (9th March, different user name: Oscar32). 

Now I want to display that visually in a sankey chart for which I need two variables: Source and Destination. This would allow me to show the flow of users between the platforms.

My question: how do I create new columns that match the phone numbers across platforms and state their platform used for the current transaction and the platform used of the previous transaction?

I hope that is clear. Let me know if you need any more informatoin to solve my issue!

Highly appreciate your help.

All the best and many thanks!!