Why am I having issues when trying to download the Phenix mobile SDKs from Github?

You may not have git LFS (large file storage) installed. Without git LFS, it will download a very small file instead of the actual binaries. The quickest way to check whether it is installed or not:
git lfs version

If LFS is not installed, see this git article for information on to install it: https://help.github.com/articles/installing-git-large-file-storage/

The git users also need to have access to our private repositories containing the mobile SDKs.