Website to download videos from Reddit
On mobile, you'll need to use the Redditvideodownloader website to download videos posted on Reddit. One of the best out there is Download Videos from Reddit, which has over 5 million downloads and great feedback from users.
The process is the same as used on websites to download to your computer. In the Reddit website, tap the three-dot icon at the top of the post, then go to Copy Link. Then open the website and it will automatically detect the copied link and recognize it.
You can now choose between HD Video Download (if available), SD Video Download and Audio Download. Note that the website indicates the space each option will take up in the smartphone's memory.