There's a method of iPhone charging (and probably most phones) that is potentially detrimental to its battery lifespan, and it's something that most people do without a second thought. Stop charging your iPhone with its case on. While some cases may not make a difference, it's better to be safe than sorry.
Apple explicitly warns against this practice on the Maximizing Performance section of its website. Scroll down far enough and it says pretty clearly (in big bold text) to "remove certain cases during charging." It doesn't specify what types of cases might be responsible for this issue, but it does note that if your phone gets noticeably hot when charging, you should take it out of that case.
