I think I have found a bug with "sPortable".
I downloaded the latest version (18.104.22.168) and installed to the root drive C:\ of a freshly installed Windows 7 64-bit. When I tried to run it a dialog box says "The program can't start because api-ms-win-crt-runtime-l1-1-0.dll is missing from your computer."
I looked into the "sPortable\App\Skype\Phone\" directory and found "api_ms_win_crt_runtime_l1_1_0.dll". Note that the filename has underscores instead of the dashes specified by the dialog box. All of the included "api_ms_XXX" dll filenames have underscores instead of dashes.
I renamed all the files replacing the underscores with dashes and then Skype started properly. This problem probably does not effect computers that have those dlls already installed locally with the correct filenames. For some reason they have the wrong names in sPortable.
The solution seems to be to rename the dlls. I hope I have explained myself properly. Thank you for your time.