Phone is Broken

Alright, so like many people, I tried to play Pokemon GO. I was playing for about 20 minutes on my break at work, and I noticed that as I was switching between it and other apps, my phone was getting pretty laggy and bogged down, to a point where the phone just froze for a minute, then when the screen turned off. I couldn't turn it on for a further minute or so. Eventually after a few minutes of this, the phone just crashed, Upon trying to restart it, it went to the odin screen, saying "mmc_read error", or something like that. I pulled out the battery and let it sit for a few minutes and tried again. It started to boot, but it was stuck on the phone's model splash screen for several minutes, which its never done before. After the phone finally got booted up, it would freeze often, and I would not be able to turn the screen back on for several minutes at a time. This has persisted all night, crashing and freezing for the remainder of my shift. After I got home I tried restarting it again, and the phone wouldn't turn on at all, so I again pulled the battery and let it sit for a while. I've done this a few times now.

Sorry it's a bit lengthy, but I tried to recreate the events of what's happened as best I could. If you need any other info just ask

I have uninstalled the game from my phone now, the phone is completely stock, no roms, not rooted. I do not recall it feeling too hot as if it had overheated

I really am not experienced with issues like this, and I really would not like to have to buy a new phone