Will iphone 5 break if I put weight on it?

Does the phone still work? If so there is a old saying-if its not broke dont fix it. In other words leave well enough alone, you might end up doing more damage to it than you realize.

For instance you might crack the screen.

I wouldn't suggest doing that because trying to straighten the phone out again might cause more damage than intended.

Always put your phone in your front pockets and never in your back ones because when you sit on your phone it can bend over time. This is probably what happened.

You put your phone In your back pocket...don't do that and don't put weight on it take it to your providers store or to the apple store and they will tell you what to do or call 1800-my-iphone