If you delete/uninstall MCPE from your phone, you will not lose your worlds. (Assuming you are on android if you're using PocketTool). The files should be under games->MinecraftPE-> etc..

Will reinstalling Minecraft delete my worlds?

Your worlds should be stored on the cloud, so uninstalling the game should have no effect on them.

Does Minecraft delete old worlds?

Minecraft has had a common issue for years, however, where worlds will sometimes vanish on their own due to a particular file becoming corrupted. If this happens to you, where you log in one day and your world is gone, it doesn't mean the world has actually been deleted. You just can't access it at the moment.