The easiest solution IMO is to download Firefox for your phone and use that instead of the YouTube app. I don’t watch a lot on my phone, but that’s what I did. Just install the Ublock extension like you would on a desktop and you’re all set. Then you can also use that instead of Chrome and free of ads on the web at large as well.

The one unfortunate thing is that you can’t uninstall the YouTube app, only disable it, and every time you go to the site it will ask you if you want to open the app instead.