You are right here but in most cases other than bitcoin, we do not have many choices to install the wallet on the computer. For example, one of the trusted wallet for storing bitcoin / Altcoins is Unstoppable Wallet and it does not have a desktop version. Also, another popular but closed source wallet is Trust Wallet and it also does not have any desktop app.
You can use a mobile phone in a safe enviroment, it is just easier to do with a PC because of the way it is designed, just as it is easy to convert a PC into an airgapped device, but very difficult, and to some even impossible for a mobile phone to be completely airgapped.
It is worth mentioning that you should not store your BTC's in the same wallet as your shitcoins, store your BTC's in BTC-only wallets that have desktop versions and use
any wallet you think is
okay for your shitcoins, that is the way to do it.