Like Phyliss, I'm a California broker but I'm also a landlord. My leases require 24 notice for showings due to the requirement that my tenants have "quiet enjoyment" of the property they rent. SOME agents have a reputation for rudeness and show up with short notice, but you have rights - including the right to deny them entry. If an agent shows up with a potential buyer standing behind them, tough luck. They should have given proper notice.
Since the agent works for the landlord, I recommend you direct your complaint to the landlord in writing and demand that they fix it. Keep a copy of everything and if you mail your complaint, use Certified Mail with a delivery receipt (little green card). Furthermore, there is nothing in your lease (check it to make sure), that says you are part of the sales team. Your private phone number should never be made public by putting it in the listing. You also have the right to tell the agent to stop calling you to set up showings. It's OK to tell the agent that you will only arrange entry through the property manager or owner. There is probably nothing in your lease (check it to make sure) that says you ever have to talk to an agent. Communicating directly with the property manager or owner ensures that they remain responsible for proper notification - they can't blame the agent for lease violations.
If you feel your landlord has violated your tenant's rights to the point of causing you harm, definately speak with an attorney.