Microsoft said earlier this month that when the new build is launched, it would include the first public preview of the universal Office apps for Windows Phone. However, Windows Insider head Gabriel Aul stated today on his Twitter feed that the next build "will take a little longer before it's available." He also confirmed that the next build will finally support the Lumia 930 and the Lumia Icon.
The current Windows 10 for phone preview build is 10051 and it cannot open any Office files as part of its known issues. Microsoft has been offering PC builds of Windows 10 to Windows Insiders at a much faster pace, releasing 10061 and this week's 10074 versions since the last phone build.
Source: Gabriel Aul (Twitter)