CloudFlare has released a new app that will route your Android device's internet traffic through its local services, effectively changing your phone's DNS. While this may be a boon for privacy advocates that bemoan the lack of DNS server choice in Android 8.1 (and below), there are a few caveats. The biggest is that the app acts as a VPN, preventing users from accessing any other VPN at the same time.
https://www.notebookcheck.net/CloudFlare-releases-an-Android-app-to-change-your-phone-s-DNS.360391.0.html