For iPhone, since Safari does not enable file downloads, you need to use a third-party app to download videos. iOS users are advised to download TeraBox from the App Store as it is totally free. Of course, you could use Chrome or Firefox to replace Safari and then repeat the same steps as Android. Access YTBvideoly with Safari Browser -> Paste URL into Input Box -> Select the Video Format and Quality -> Hit "Download" button -> Save Video to TeraBox