What exactly do you want to tell us, tommytrant20?
I guess that you'd like to seek advice for downloading online free videos (from YouTube probably) to your mobile phone.
For software, 4K video downloader is great, but it's not free, and it just supports limited output formats: MP4, MKV, OGG Theora, MP3, M4A. If you want an freeware, use MacX YouTube Downloader as a nice alternative.
For extension, SaveFrom.net helper is the one, fastest, easiest, download HD, download from web homepage, etc.
You can try them all and select what suits perfect for you, my friend.