Maybe there is a translation glitch, but I’ve never seen an iOS device complain about insufficient memory. Is the message actually about storage?
If it is then you can review what is using your storage via Settings > General > iPhone Storage. Photos is frequently a culprit for taking lots of space and there are a couple of ways of mitigating that - the easiest being to use iCloud Photos and then have “Optimise iPhone Storage” turned on.
If the error message really does mention memory, then it would be likely be indicative of an app with bad coding that has a “memory leak”.