Why won’t my phone won’t charge?

This could be due to a lot of things. Are you charging it with a lightning cable? or wirelessly? Have you tried other cables?

In my experience, issues with iPhones not charging, is often a result of debris stuck in the charge port, but without more details it's hard to say anything definitively. However, I would check and see if your lightning cable sits flush with the bottom of the phone when you plug it in. If it doesn't plug in all the way, or sits sort of askew, I would have a look into the lightning port with a flashlight.