Front/back camera and ear speaker not working after battery replacemen

I replaced the battery of my moms phone yesterday (iPhone 6s Plus). It is the second time I was doing it after buying the phone, so it didn’t give me any challenge , or so I thought. After turning on the phone, I did a quick check to see if everything was working. Both cameras was working, and also the ear speaker at that time.

I ran an update and connected the charger. When the update was done, I noticed the phone was very warm, and the battery had only charged a couple percent. I disconnected the charger and noticed that the charge dropped faster than normal. At that time I accidentally opened snapchat and saw that the front camera did not work, and the same with back camera.

I turned phone off and opened the phone up again. The battery it self was too warm, but right side of the phone was. Disconnected the battery cable, and also the three cables from the screen, and put the phone back together. Still, the cameras did not work, and also noticed that the ear speaker did not work after getting a call.

On a positive note, the phone did not get too warm, it did not loose charge as fast as it did, and the battery is charging normally. So the phone is useable, except for the cameras and the ear speaker. Also noticed that led flash/light was gone as well. The light sensor is working though.

Since I was the one screwing up, I have ordered a new phone (but I can send it back if I get this fixed). Looking at previous topics here, it might be that the culprit is the unit holding the front camera and the speaker, and replacing it might also fix the back camera. Looking online, I can buy the whole screen with all the parts assembled, it did not cost too much more than the front camera and speaker unit, and it will be easier to replace. What I wanted to ask before ordering it is what change of success would be. Since the camera did not fail right away, but afterwards, could it be something else that is wrong? I suspect that the phone getting warm and eating battery could be the cpu working hard for some reason, maybe a loose cable and that could have destroyed something else?

I would appreciate your thoughts on this.