This used to be very easy on both Android and IOS before youtube decided to release youtube red. Luckily there is a workaround.
It is pretty much same for both android and ios. 1. You need to use chrome.
2. Request desktop mode
3. Start your video
4. Go to your home screen
5. Your video will pause slide to audio options and resum
6. Thats all enjoy!
Credit to linked video:
https://www.youtube.com/watch?v=wr7Gy7VINB8&app=desktop
