I hate this..... Unless one is male and one female or one goes by a nickname, it's a pain.
Go through the phone call and hope... Then, at the end, when setting the appointment and are confirming names, you can say something like, "I'll ask for you when I get there. I presume you are the only "Bob" and they'll know who I'm talking about?"
It's awkward, but, when they ask for your contact information, you can confirm the apartment community's phone number ("Is this the best number to call to reach YOU?) and ask for the leasing agent's last name.
If it's the right person, you're lucky. If not, you need a new alias.
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