If the battery is getting hot, it's likely because there is a large current drain occurring (something on your phone is drawing excessive current).
Let your device cool off and then start by disconnecting the screen assembly (follow this guide) and then connecting your phone to an iTunes enabled computer, preferably with a genuine Lightning cable.
Leave it in that condition for 30 minutes to see if the battery still gets hot. If not, then add the screen (LCD & Digitizer) and then the front camera & sensor flex until you isolate the issue. Repair or replace as necessary (or get back to us with more details...make sur update your question or comment on a specific answer so we get notified).