Why is phone my phone constantly restarting

Your question is a little hard to understand, but I'll do what I can to try and help.

Okay, first of all, you say your phone is constantly restarting. That's generally referred to as a boot loop and happens to iPhones when there's something significantly wrong with them. I'd like to clarify that statement, because there are a couple different kinds of boot loops. The first one is where the phone doesn't have a chance to boot; usually you'll see the Apple logo come on, then before you even see the passcode screen, the phone will restart and repeat that cycle forever.

In the second kind, the phone boots all the way up and works for exactly three minutes. That's the amount if time between when the phone scans its sensors and when it finds one with a serious error, it restarts the phone in an attempt to recover. However, once it reboots, it goes three more minutes then reads its sensors and finds that same error, whereupon it reboots again.

If it's the second kind then we can figure out what's going on with it much easier than with the first kind. It gives you enough time to read the logs that are stored on the phone whenever that reboot, called a kernel panic, happens. Here's an article on how to find those logs and what they mean.

iPhone Kernel Panics - iFixit

If it's possible for you to do so, go in and find the latest panic log then come on back and post the first page of it to your question so we can analyze why it's rebooting. You can cut and paste the text or capture a screenshot; here's how to add a picture to your question.

Adding images to an existing question - iFixit Repair Guide

Finally, you state that you have to open your phone to charge it. How exactly does that work? What good does it do to open the phone and how does that allow you to charge it?

At this point my first guess would be to suggest that it may be a problem with the charging port flex cable assembly, but without more information it's impossible to say for sure.