I was thinking in nostr terms. I think, nostr and bitcoin needs different usecases, therefore different security solutions are there.

In bitcoin, probably you dont need to use your privatekey that often. So having a multisig setup is good, and advised.

However for nostr, you use your keys way more often, and you might want to use it not only at home, and you might not want to take your multisig setup around to post on nostr e.g.

The proposal of using phone is just a simplification, but with similar security guarantees as a signer, if the phone has a secure element with unextractable features (meaning your key cannot leave the device, it has to be used to sign). Of course this unextractable feature depends on the phone itself.