Why is my iphone 4 not charging?

I'm having problems with getting my iphone to charge. I've tried different things such as: cut the phone on and off, plugged in different chargers & tired using different wall outlets, plugged it up to the computer, and i even tired my mom iphone on all the chargers and hers seem to work perfectly fine so it has to be my phone. Does anyone else have or had this problem and what did you do to solve it?

I had this problem before and that is because you have problems with battery or phone. Make a "diagnostic problem" and then see it.

Have a look at the charging port, check there's no fluff ect in the way. If it looks a little green atall that'll be liquid damage, also under the charging port in the center there's a liquid indicator which should be white, pink/red is no good.