Forwarded Call Alert needs to access the phone state and device logs, and requires root permissions for the latter.
The app does not have Internet permissions and does not send any information by itself. If you use the "Request device support" feature, the app will collect a system log and send it via email to the app authors. Phone numbers will be cleaned from the log, but it can contain other sensitive information, including personal data. The submitted logs will only be used to test for potential device support for call forwarding data, and for no other purpose. They will never be shared with third parties.