1) I use a trust wallet to store crypto. My question is how safe it is to store over $20k coins? Yes, of course, I take care of keeping my mobile safe and virus/malware free so never click on any unknown link as know about his as i am in IT field.
This is subjective. Even if you don't click on any links, run any suspicious software, there are still ways to compromise your computer without and zero day exploits are not uncommon as well.
2) What if I lost or damage my hardware wallet? Do i need to buy same hardware wallet and restore my coins? or can use private keys in any other online wallet and get my coins back?
You shouldn't use online wallets. You will be given the seed at the initialization of the hardware wallet. That can be imported into many of the compatible desktop wallets to restore all of the addresses.
3) What if the hardware wallet is damaged or corrupt?
Same as above. If you'd like, certain hardware wallet provides a limited warranty to cover for damages.
4) Instead of hardware wallet can I keep the separate phone to store my coins in wallet app like trustwallet and keep disconnecting from the internet unless i want to do transaction. Is this a better choice?
Not really. Hardware wallets are operated in a sanitized environment and it is difficult to compromise that environment. This is why they are secure, because they are designed for specific tasks and are intentionally secured to execute and accept certain commands.
Disconnecting your internet periodically actually does nothing to improve your security. Malware would just wait for an internet connection to relay any data back to their C&C. Your best case would be to ensure that the wallet never gets online and use another device to send the transaction data, aka. Airgapped wallet.
