Is the only way to "search" across my tasks on the iPhone app to create a filter? I am a premium member.
Yes, this is currently the only option to search through your tasks on the iOS app, but we'll consider adding a free search feature in future updates.
You're welcome to vote for this request in our Votebox: http://todoist.com/Vote_iOS/showProposal/67/
That's a really painful way to do something which should be really easy.
Also, when you finally find something with a filter, it should show the
subtasks of the found tasks.
My reply was from October 2013 and right now it is already possible to search on the iOS app :-) To do so, simply drag the task list down to reveal the search bar at the top.
We'll improve the display of sub-tasks in future updates.
Oh cool! There are a ton of questions related to this in your help center. I'm thinking it would be good if you went through them and replied with what you replied to me, so people don't make the same mistake I did.