The tighter the pants or the pocket in them... the more likely the possible damage that could happen. Even an expert couldn't guess at how much or little damage may have happened unless they get to inspect it... so anything you get told is only a guess. I'd say if it is working, then you are probably ok, just pay attention to it and how things work in order to figure out if something is messed up.
Since this is a user caused problem, the manufacturer wouldn't cover it as a defective warranty issue... only one of the add-on warranties that cover user abuse would if you had purchased one of those.
It's possible there is damage you missed seeing...like the tiny alignment pins getting broken that are often used on components these days... It's also equally possible ( at this time ) that what you heard was just the parts rubbing against each other... remember they are held together pretty tightly and when forced, they would suddenly shift against each other possibly causing a cracking sound when they do.... So a sound like a crack can happen when nothing breaks, we just can't say for certain either way.
I've seen a Samsung Galaxy something or other that was pretty bent and the front lens/glass completely cracked all over... the phone is still working other than that. Of course it's hard to read most of the screen... but it does work.
While I do wear relatively loose jeans... they still don't have enough room in the pockets to sit if my phone were in them. I'd also have the same issue of remembering to remove my phone when I sit... so I use a holster instead. A holster isn't a 100% solution either, they can catch on stuff ( like seat belts for one example )... so no matter what you do... you still have to pay attention.
