The latest Insider builds on the desktop are for Redstone, the next version of Windows 10, but these builds still have to hit the mobile side.
This does not mean they are not in internal testing, as WindowsMania.pl has been able to confirm. They have been able to install the latest Windows 10 Mobile Build 10.0.11102.1000 on their Lumia 640 XL but reports that the software is still pretty raw, with fantastic battery drain (giving a standby time of only 5 hours!) and with audio not working at all.
Microsoft had earlier said the first builds of Redstone will not have many new features, with will instead concentrate on deep changes behind the scenes to the Universal Windows Core to enable future scenarios.
The implication of the news I think is that despite Microsoft’s promises for a more rapid roll-out of Insider Builds this year we may still have a bit of waiting to do before Redstone hits our Windows phones.