pretty sure from the phone you cant unless you use the browser and not the app not sure tho if its within a certain amount of time you can click hide on the op and it removes the thread from the general public view but the content is still there for the mods to see the same thing goes for posts
This ^^^ Hiding the OP hides the thread... I'm pretty sure you can hide posts from the app too, I'm just not sure how to do it, as I don't use the app...