Asking him nicely should be enough. He should be as eager to spend time with you as you are with him. If it isn’t, consider the bigger picture. Are you feeling neglected in any other ways? Is this really about his phone or is that just an easy thing to blame in order to defer something more problematic? Open communication, kindness, patience and love will get you where you want to be. Good luck.
Start a project, that needs his strength, maybe put in a new tree, either for yourselves or others and help the atmosphere as well x
Finding something you really enjoy practicing, like meditation, yoga, gim atc.. Something that connects you with yourself because most of the time we spend on phone is to avoid to think about our feelings or responsibilitys. When you find something that completes your soul, you no longer needs your phone, so ya, do it.