To export the call log for all of your sub-accounts, to go Calls ▸ Export Calls.
In the Export Call Data screen, enter the email then scroll down to the Filters section, Toggle the box Export all calls for all sub-accounts.
In the Fields to Export section, select Account Name and Account ID.
Click Build Report.
An email will be sent with the call log from every sub-account and the spreadsheet can then be sorted by Account ID or Account Name.