Apple has released a minor iOS 12.3.1 bug fixing update with fixes for VoLTE and Messages app. iOS 12.3.1 comes almost two weeks after Apple first released iOS 12.3 packing plenty of features and enhancements.
Among other things, iOS 12.3 included a revamped TV app, added AirPlay 2 support for Smart TVs, introduced Apple TV Channels, and more. iOS 12.3.1 is a small update that is mainly aimed at fixing some of the bugs that made their way into the OS.
– Fixes an issue that could prevent making or receiving VoLTE calls
– Fixes issues in Messages that could cause messages from unknown senders to appear in your conversation list even though Filter Unknown Senders is enabled
– Fixes an issue that could prevent the Report Junk link from appearing in Messages threads from unknown senders
iOS 12.3.1 update is already available for all compatible iPhones and iPads. You can download it from Settings -> General -> Software Update.