How to implement machine learning models on mobile phones?
I think I'm qualified to answer this because it was yesterday that I viewed Google's "DevFestOnAir 2018". There was an "End to End Machine Learning" talk where the speaker mentioned what TensorFlow(TF) has to support AI in mobile devices. 
Now, TF is available for JS , Java and many other languages, so this captures the entirety of the model that runs on your PC, uses other functionalities to make it run on lesser RAM and Processors. Do check this out. If I'm not wrong TF has a feature that would do the conversion for you.
I've built Machine Learning Models Random Forest and XGBOOST on Python or R
How can I implement that my model work in mobile phone IOS / Android? Not for training, just to predict the probability for users by properties and events.