Beta testers who are members of Apple's beta testing program will receive the iOS 11.2.5 beta update over-the-air after installing the proper certificate on an iOS device.
Those who want to join the beta testing program can sign up on Apple's beta testing website, which gives users access to iOS, macOS, and tvOS betas. iOS betas are not always stable and should not be installed on a primary device.
No new features were discovered in the first developer beta of iOS 11.2.5, so it's not entirely clear what new features this beta introduces.
It's possible it focuses primarily on security improvements and bug fixes, and if that's the case, we may not know the extent of what's in the update until it sees a public release complete with detailed release notes.