Hi Tam03,
Thanks for reaching out in Apple Support Communities. I understand you're unable to access and use emoji's on your iPhone. I'll be happy to help.
You've done an excellent job with the troubleshooting steps that were performed. You mentioned deleting and adding the emoji keyboard via Settings. Just to be sure, did you go to Settings > General > Keyboards, to delete and add "Emoji"? If so, you'll want to open the Messages app, then with your finger, hold the globe icon for a few seconds and let go. Check to see if "Emoji" appears in the keyboard.
In addition, you'll want to make sure your iPhone is updated to the latest iOS update of 13.3. This help isolate the behavior you're experiencing further and helps improve the software on your device. If needed, here's how to update the software on your iPhone: Update your iPhone, iPad, or iPod touch
Kind regards.