Some people are wondering if Tensorflow Lite would support CoreML / iPhone's neural engine. Tensorflow is not supported with coremltools (but I suppose Google could contribute a patch for this). I'm not sure about the CoreML libraries on the phone but from my understanding it may work.
Keras is supported out of the box with the Tensorflow backend though. See https://medium.com/@JMangia/super-simple-end-to-end-test-of-... and https://github.com/apple/coremltools