To view the videos on your mobile phone you should download and install a VR Player of some sort, there are several apps for that, Android and iPhone, but we recommend these free ones for the respective platforms:
Android:
https://play.google.com/store/apps/details?id=com.vimersiv.vrplayerfree
iPhone:
(paid)
https://appsto.re/il/-51F_.i
(free)
https://itunes.apple.com/il/app/vrplayer-2d-3d-360-video/id1058724046?mt=8
Windows or Mac:
http://www.kolor.com/gopro-vr-player/download/
VR Media Player (Android only):
https://play.google.com/store/apps/details?id=com.xojot.vrplayer&hl=en
After installation you should try and test these settings, depends on the video you are trying to watch (these are the ones we recommend for our rendered videos):
FOV - 120°
Top\Bottom
Spherical projection
Enter your phone into the headset and enjoy!
Make sure it sits right and has no chance of slipping out.