VPN / iPhone / Setup / Help

I'll keep this as short as possible. It's slightly complicated - but not really.

At home, I have an AT&T Fiber Modem which is also a wireless router.

I also have a Cisco Router that automatically makes a VPN connection back to my office. This router also has a wireless connection and POE Ports.

So, when I'm home and want to be on my home network, I connect to the AT&T WiFi. When I want to work, I connect to the Cisco Router's WiFi. I also have a Cisco Phone connected to a POE port on the back of the Cisco. All of this works fine.

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In my office, I have a computer that I use for both work and pleasure and I switch between the wireless networks depending on what I'm doing. I want to move the Cisco phone to my office.

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I have an ASUS RT-66U Wireless Router I have put into Bridge Mode. It connects back to the SSID of the Cisco Router.

I have the ASUS plugged into a small Netgear POE Switch. I have the phone plugged into the same switch. Phone powers on but will not connect back to the phone system in the office. Any idea's on how to get this to work? Thank you in advance for any help you can provide.