Updated: Microsoft has now released Windows 10 Mobile Build 15063.2 to insiders in Slow Ring after releasing it first to Fast Ring. As you may know that Build 15063 is the Creators Update RTM Build and now Microsoft will push cumulative update builds to Build 15063.
The Build 15063.2 enables ability to update to Creators Update RTM Build 15063 from Anniversary update on Windows Phones.
Windows 10 Mobile Build 15063.2:
We have released Windows 10 Insider Preview Build 15063.2 for Mobile to Windows Insiders in the Fast ring. This build includes a single fix to enable the ability to update to Build 15063 from the Windows 10 Anniversary Update (Build 14393) on Windows phones.
You can read our categorized changelog to know what new changes and features are coming with Windows 10 Mobile Creators Update.
Microsoft is almost confirmed to release Windows 10 Creators Update on April 11.