To help you visualise where we are in terms of the window for these monthly OS updates, here's a helpful chart:

Now that the Fall Creators Update ('rs3', at least in name) is the 'production' branch of Windows 10 Mobile, we are seeing 'Patch Tuesday' fix round-ups for it too, with the official list for 15254.248, the 'February 2018' update' mainly composed of minor fixes and security patches, at least in terms of mobile relevance.

From the official release notes:

• Security updates to Microsoft Scripting Engine, Microsoft Edge, Microsoft Windows Search component, Windows Kernel, Device Guard, Windows storage and file systems, and the Common Log File System driver.
• Addresses issue where the touch screen would remain unresponsive. In most cases, using the Power button to turn the screen off and on restores responsiveness. Occasionally, at startup, the touch screen would remain unresponsive, and the only recovery mechanism was to restart the phone.

Again, it's still significant to see this arriving (near*) simultaneously for 'mobile' in lock step with 'desktop', in terms of the under the hood modules. And, as usual and as per the graphic above (the rectangles in a shade of red), all other supported Windows 10 Mobile branches are getting updates too, so all those older phones (Lumia 930, 830, 735, 640, etc.) finishing life on the Anniversary or Creators Update (if the user was smart enough to go via the Release Preview Insiders ring!) aren't losing out on the core security fixes, at least.

* Curiously, for the first time ever, a hitch at Microsoft's end caused Patch Tuesday to roll into err... 'Patch Wednesday'! The release was supposed to be .249 but clearly there was a problem and so the previous build was pushed.

UPDATE: .249 seems to be hitting some phones as an alternative. Who knows why some phones are still getting offered .248? Suggest no one loses sleep over the difference, anyway!

As usual, in today's vulnerability-stricken, malware-strewn and fraudulent times, we should never disregard security fixes (e.g. to the Edge browser) though, so update today in all affected mobiles, just in case!

Phones on the Creators Update should advance with this release to build 15063.909 (from .850) phones on the Anniversary Update should advance to 14393.2068 (from .1944). In each case you get the core security and component updates, though obviously without any subtleties in functionality introduced in later branches.

As ever, with all phones, head into Settings/Update & Security/Phone update in order to get the update immediately.