1 - Create a pivot table, and then use the Phone Rep field as a category and the Phone call Duration in Minutes as field as series
2 - Set the formula for phone call duration in minutes to Average and add a pie chart linked to the pivot table
3 - Export the custom view to an Excel dynamic pivot table
4 - Save the spreadsheet and upload it back to the system.
Reference:
https://docs.microsoft.com/en-us/powerapps/user/export-excel-pivottable