I don't have this problem with my phone whatever videos I am watching. It's a good idea to optimise your phone from the Devive Care app before using apps that use much CPU or RAM and battery, also you can download Good Guardians app and it will help you with optimising your phone even better. Credit to GusB who recommend it on this forum. Also restart your phone once or twice a week and go on Settings>Apps> and clear cache manually for Netflix. Unloading your phone of residual data makes it smoother. Also make sure your Internet connection is good.