Hello leerkc,
welcome back to the Polycom Community.
Just as an FYI the SSIP7000 can only have 2 separate calls in a conference in addition to yourself.
If you only have one call with yourself in a conference the other party can call the SSIP7000 and you can answer the call and simply select JOIN (may have to press more) and add this party into the conference.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Best Regards
Steffen Baier
Polycom Global Services