Days after the release of iOS 12.3, Apple has started rolling out the new iOS 12.3.1 for iPhone and iPad users. The update weighs about 117 MB in size, and by the size of the update you can tell that it is not a big release, however, per the changelog, it does bring some important bug fixes to the devices.
There are three essential bug fixes that iOS 12.3.1 brings. First of all, it fixes an issue that prevented some iPhone and iPad users from making or receiving VoLTE calls. The update also fixes the problem with the Messages app, wherein messages from unknown senders would appear in users' conversation list even though Filer Unknown Senders was enabled.
Finally, the update also fixes an issue that prevented the Report Junk link from appearing in Messages threads from unknown senders.
Like mentioned earlier, the update isn't a big one, however, it is still recommended that you install it as soon as possible, especially if you were affected by any or all of these bugs. If you are running the older version of the operating system and don't have these mentioned bugs in your phone, unless updated, your devices will remain vulnerable to these issues.
While you will receive the update automatically over-the-air, but if you don't, you can also run the update manually by heading Settings>General>Software Update.
And if you are yet to install the iOS 12.3 as well, here are all the details on its changelog.