In simple words, we can say that the coins are on the blockchain and they will never leave it, and the hot wallet is just the door, which I must have it's key to open it.
Keep your private keys to yourself - that's only when you can say that you possess your Bitcoins. Never give it to anybody, even don't use it over websites that ask you for the same to claim some (or same) amount of alts (eg.: Bitcoin Cash) unless it's official. I had my private key compromised once due to using it online over a website.
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that's means I don't have to worry if my phone damaged or gone to space as long as I have the recover key 
If you'd like something more easy, try wallets like Electrum. Even if you don't have your private key, you can access to your "wallet" through your recovery seed when you import it on a different device. Wallet - consists of addresses (each of which possess its own private key). So, storing too many private keys could be too much hassle and having a 12 words recovery seed can help save you from that.