Help! Cannot open my files

I need to open a very important file on my iPhone but it keeps saying “cannotOpenDatabase(Error Domain=SqliteErrorDomain Code=13 "database or disk is full" “ I barely know anything about tech stuff so I bought the cloud+ hoping that it would help me (In case it was about my iCloud being too full) but that didn’t work either! I tried deleting files but that message keeps coming up. Please help. I need to open this file asap. Help would be greatly appreciated