There are no static IP addresses for outgoing traffic from applications running on PWS. Even if there were, it would not be safe to whitelist them because outbound traffic from all apps running on a Cell would appear to come from the same IP.
https://community.pivotal.io/s/article/The-original-IP-addresses-for-the-requests-made-by-the-run-pivotal-io-CF-applications
There are services which can allow you to do this though. QuotaGuard is one.
https://docs.run.pivotal.io/marketplace/services/quotaguard.html