Facebook’s Messenger app has a thumbs up button that, when tapped, sends a Thumbs-Up emoji (Or sticker?) to whoever you’re talking to. Using it is even better than typing out ‘K’ in place of ‘Ok’ or ‘Okay’ and it induces far less range on the recipient’s side when it is sent. The thumbs-up symbol, not to mention the thumbs-down which Facebook doesn’t support, is pretty universal in meaning. You can use it to communicate approval and disapproval but only Facebook capitalizes on it. Thumbify is free a third party keyboard app for iOS with exactly two buttons; a thumbs up and a thumbs down (and a pretty pointless number pad for some reason). Once enabled, you can use it to quickly send the thumbs up and thumbs down emoji when texting.
Install Thumbify and enable it as a keyboard from General>Keyboard in the Settings app. Switch to the keyboard when texting to send a thumbs up or a thumbs down. Tap the 123 button to switch to the num pad if needed.
I’m going to go ahead and state the obvious; Thumbify is using the same thumbs up and thumbs down emojis that you can find in the default emoji keyboard. The emojis are already there on your phone but the app makes them exceptionally easier to access. If you’re in the habit of using these two often, they will show up in the recently used emojii tab negating the need for this app. For me, it’s pretty useful because unless it’s easy to access, I will forget about it. The app is free and will only cost a little space on your phone to try.