I got a warning message that mobile data was exceeded. Will this add additional charges if the phone is being used? Or do i need to free up space?
You might need to ensure that the mobile data plan data warning settings match your plan, and verify your metered usage with your carrier.
Freeing up space on the phone won’t have an impact on mobile data, no, so not needed unless you’d like to or you’re running low on storage.
As @Saijin_Naib mentioned, freeing up space is not related to mobile data. As of now, only warnings are sent and the actual limit is not enforced. In the future, the actual plan limits will be enforced at which time you will be able to “top-up” or upgrade your data plan.