Your ISP will also know that you are using Casa, though they won’t know exactly what you’re doing. Traffic between your device and Casa is encrypted, but they know that requests are going to Casa’s servers.
If you want to improve this aspect of your network privacy, then you’ll want to use a VPN on your phone and other devices that you use to interface with Casa. This way, your ISP only knows that you’re sending traffic to a VPN server. Since you’re still trusting a third party (the VPN service) to not spy on your activity, this isn't perfect privacy.
If you wanted to take your privacy a step further, you’ll want to configure Tor clients on any device that you use to interface with Casa.
Another reason you may wish to use a VPN or Tor is due to logging.
Casa has no intention of logging IP addresses of clients who connect to our servers, but if you want to be 100% certain that your IP address never ends up in any logs, it’s best to use a proxy of some sort. Also, because we use Cloudflare, it’s possible that your IP address will be logged by them — we have no control over their logging. By not connecting from your real IP address, this becomes a non-issue.