When you zip a file, it appears to be a very final sort of act. On the surface of it, the zipped file appears to be a closed off container that nothing can be added to but you can add files to an existing ZIP file pretty easily. Here’s how. Add files to existing ZIP
How to Unzip a Zip File With Your iPhone or iPad’s Files App
The Files app, added in iOS 11, supports zip files. You can open them, see their contents, and extract files without any third-party apps. You’ll still need an app from the App Store if you want to create zip files.