That is a good question. I don't think any hardware wallets support Steem or Steem Dollars right now so that's not an option (someone please correct me if I'm wrong on this). There is probably a way to sign transactions on an offline computer but that would be far from simple. So, there is no great solution. Which was kind of my point in asking the question - to point out that whether you use an active key on a phone or a computer you are vulnerable to attack.

Bonus question: Where did you get your owner key? Was it generated on an offline computer (guessing not) ... because if it wasn't that is at risk too.