Flip clip is an application that can make animation frame by frame on mobile devices, which can reduce the threshold of animation to only one mobile phone.
 

Flippaclip provides a very simple way to make animation. You just need to draw one frame at a time... Yes, one frame at a time. The built-in tools include paintbrush, Lasso, filling, eraser, multi-function ruler, adding text and supporting Apple pencil. Up to 1080p video.
 

The free version of flipclip supports up to 3 layers, and 10 layers can be unlocked for payment. However, if you really want to be productive, you'd better use it on iPad.