There are several ways to download a YouTube video on a phone:
Use a third-party app: There are several apps available on the Google Play Store that allow you to download YouTube videos. Some popular ones include TubeMate, VidMate, and Snaptube. However, these apps are not available on the Apple App Store.
Use a website: There are many websites that allow you to download YouTube videos. Simply copy the URL of the video you want to download and paste it into the website's download bar. Some popular websites include y2mate.com, keepvid.com, and savefrom.net.
Use the YouTube app: The YouTube app itself allows you to download videos for offline viewing, but this feature is only available with a YouTube Premium subscription.
Please note that downloading YouTube videos without permission may infringe on copyright laws and can lead to legal consequences.