There is a way.
I have tested this tonight and works flawlessly
On your device, go to the App Store and search for "Document 5
" which is free.
Once installed, launch it and tap the bottom-right icon that looks like the Safari icon (a compass).
This will display a web browser where you can search for 'savefromnet' without the quote marks.
Tap on the 'en.savefrom.net' link in the search results.
You need to get the URL - the address - of the YouTube video that you want to download. One of the easiest ways is to launch the YouTube app on your iPhone.
Find the video you want and wait until any advert has finished playing and the video starts. Tap on the video to show the controls and then tap the share icon (an arrow pointing right).
You can then tap Copy Link.
Now return to the Documents 5 app, and tap in the white box to select it. Tap again to bring up the Paste option and tap that to paste in the URL you copied from the YouTube app.
Tap the green tick and you will see a list of various resolutions, so you can choose the quality you want.
Tap the green Download link next to your preferred quality and rename the video if you want to. Now tap Done amd the video will download. It's best to only do this via Wi-Fi as videos can quickly use up your monthly 3G or 4G data allowance.
Once downloaded, you'll see the video in the Downloads section of the Documents 5 app.
You can save this to your iPhone or iPad's Camera Roll (not the native Videos app, unfortunately). To do this, tap and hold on the video and drag it up until you see the folder list. Keep holding and drag it into Photos and then into Camera Roll.
Now you can just head to the Photos app and watch the video.