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:
Windows or Mac:
VR Media Player (Android only):
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°
Enter your phone into the headset and enjoy!
Make sure it sits right and has no chance of slipping out.