Hardware wallet is best place for saving Bitcoin fund, but its not really necessary when you have option holding assets in free wallet like Trustwallet or any mobile phone wallet.
Mobile phone wallets are one of the least secure ways to store your crypto and it should be only used as a hot wallet due several reasons; first, mobile phone (especially android based ones) are prone to malware attacks and 2nd, you open yourself to a $5 dollar wrench attack.
I have been several years with cryptocurrencies and still not use hardware wallet for saving bitcoin, most time hold and save bitcoin in exchange account.
If mobile phones are one of the worst places to store your crypto, then exchanges (and other centralized platforms) are the worst possible place. You are playing a very dangerous game if you think that your bitcoin is safe there after everything that has happened lately and milions of people losing their money because they used exchanges as banks (which they obviously aren't). After all, its far cheaper to learn from other people's mistake than from your own.