Being denied SSDI at this time does not mean you are automatically denied SSI.

Though you may not have enough evidence at the time you submitted your claim for SSDI to get it, (which you could submit an appeal to provide more evidence, you still possibly could qualify for SSDI), there is enough evidence to think you may qualify at this time for SSI and are doing the phone interview to verify some things to put your application through for SSI in the interim, whether or not you file for an SSDI appeal. You still may not qualify for SSI, but that is what the phone interview will help determine. There is a really good chance for it though.

If you do decide to file an appeal for SSDI, would highly recommend getting an attorney to help with this. There are no fees upfront as they work on contingency, collecting fees only if they win your case.

Wishing you well on your interview. Good luck!