Imovie on iPhone not keeping up with the cloud

First I apologize, I’m not the most tech savvy, so I appreciate any input. I do a lot of editing on iMovie and I’m currently on a 11plus and yes, in the process of updating and/or buying a new phone, but I haven’t understood this for the longest time.

So when editing in iMovie, to my understanding everything is saved in the cloud. So, if I’m in the process of editing one movie over a long period of time and I delete videos later in my phone folder, aren’t they still saved in the cloud if they are already in iMovie.

As I clear up space and coming back to it later, iMovie says how I deleted footage, but I thought it would be in the cloud, correct?

Again, I know this is is simple for a lot of you guys and I’m just trying to figure it out and I appreciate any help in advance you can provide, so I can prevent this later.