PDL flash module does not have APIs to erase sub-sector and sector. Even the architecture TRM does not specify the system calls for those operations.
Please confirm if these operations are possible. Please provide the APIs for the same.
You may have APIs to do to erase sub-sector and sector with the release of ModusToolBox 2.0.
ModusToolBox 2.0 will be released by the end of this quarter tentatively.