with trezor. you cant just press a button on the device while walking around town to send a TX.
you cant even just plug it into any random persons computer and use it instantly, you need to download the browser extension and log in.. which is a security weakness. (imagine a virus that can detect a trezor/webextension and replace it with a malicious version to send funds to them blackhat instead of the address the user types in)
i think phone app wallets are pretty much on par with a trezor.. no better, no worse. however we are still in the innovation stage and things will get better and more independent, away from third party services
It is safe to use a Trezor on a compromised computer. The private keys are never revealed, and a transaction cannot be modified because it is signed by the Trezor and verified by you. A phone wallet is not as secure.