Try Blue Wallet as your mobile companion app for your Jade. It's easy to set up, use, and has all the features you need.
Put aside safety concerns when you think of watch-only wallets. As has been stated, they don't have the private (signing keys) for your bitcoin. if someone were to steal your phone/computer or gain remote access to it, they can watch and see how much bitcoin is in the wallet, but they can't steal it due to the lack of private keys. This is true for watch-only wallets regardless if you use them on a phone or a desktop.
Since you are new to all of this, I suggest you read Blockstream's Help Center about the Jade. Go through all of the articles. It's for your own good. You don't always need a video to understand something, especially if a quality one isn't available.