On this project I was lucky enough to work with the Google AI Edge team who have deep expertise in edge deployments on device. Check out this app they built which loads in the Gemma 270m models and runs them on your phone.
https://play.google.com/store/apps/details?id=com.google.ai....
You also can finetune your own models and load them onto device with the same workflow. Scroll to the bottom to see the instructions and a screenshot example https://ai.google.dev/gemma/docs/mobile-actions