Bedtime is rarely the best moment to argue about rules. Games keep offering another round, another reward, and another reason to stay awake.
A calmer setup is to reduce what can open at night. Keep bedtime-friendly apps available if needed, and lock games, downloads, social apps, and sensitive system entries before the evening routine begins.
Game limits work better when they are prepared before the child is tired. A bedtime group can make the phone useful without making games available.
iPhone Locker helps parents create this kind of mode, so the same evening boundary can be used repeatedly.