Format ext4 doesn't make much sense on USB stick, is there a particular reason why you would use "system" format for USB?
As nrt wrote if you format your flash disk in your phone the format would be fat32, which is fine, but the limit per file is 4GB.
Based on your choice to format flash disk to ext4 I'm assuming that you are using a Linux distribution.
So you can either use exFAT, or use fat32 and split the file before copying with split command. You can merge it later with cat command.