You don't have to use/call the SROM APIs. PSoC Creator and the PDL code that comes with it, provides handles/access to all the SROM calls required for accessing Flash/WFlash/SFlash. It should be noted that only through these handles (or the equivalent code) you can access the SROM APIs and not directly.
Refer to the Flash driver documentation in the PDL documenation (available in PSoC Creator > Help > Documentation > Peripheral Driver Library). file:///C:/Program%20Files%20(x86)/Cypress/PDL/3.0.1/doc/pdl_api_reference_manual/html/group__group__flash.html
Let me know if this helps.
Meenakshi Sundaram R