If your anything like me, you've been searching high and low for a simple solution to mount an external mic so you can actually hear things from your OSMO recordings.
I've seen a 3d printed solution that seemed ok, but I was concerned with the reliability of it.  I found a video of a guy who cut the top of a large pill bottle and fashioned it around the handle with a 3/8 adapter attached.  I was actauly about to purchase a small 3/8 ball joint and super glue it to the back of the phone mount.

Then last night, I was catching up on my Fstoppers articles and there it was!  
I knew there had to have been an existing mount that would work, and sure enough, Joby makes one.

Its only $10, simple and available from BHPhotovideo.com

Joby phone clamp + 3/8 to 1/4-20

Credit: I Found this posted in an article on Fstoppers.com, if you dont already read Fstoppers, and you take videography/photography seriously, it is a phenominal resource.
Good luck out there!

Thanks for sharing... So it is Joby's that is extremely small.
Note your phone's wide before purchasing Joby. My phone (Meizu M2 Note) is quite large, 3" wide. Must use Joby GripTight XL version for 2.7-3.9" Wide versions.

Just found out the L-type smartphone holder grip (known in local market as 'Tongsis L holder') can also work (Previously thinking to use it for top-mount, and didn't work, but doing this way can work).

Set

It's a good solution, thanks for sharing.