Curb Your Smartphone Addiction by using Forest. https://www.forestapp.cc/
I have been using this APP when I need to stay focus. Because it helps me to leave along with my phone for a while and whenever I want to stay focused, it plant a tree. And the tree size depends on the time I stop using the phone. Leaving the app halfway will cause my tree to die. I think it somehow can help people to stay away from their phone by the tree plant achievement. Once you set up the timer, you cannot use it, even you leave the app, it gives you the warning message. You can also noticed that the top right corner has the total gold coin you had earned so far. However, you should always set up the break time, it reminds you how many minutes left, so you can move on to the next maintain focus time.
Here is the screenshot when I set up 25 mins goal, once I didn’t use my iPad during this 25 mins. The App will plant a small tree for me. And you can always go back to check your past achievement by counting your tree and summing up your time.