05-08-2017 I would suggest you make sure your computer is on the same VLAN as the phones, and that you verify on the Polycom VVX500 what the IP address is for the hardware --- using IE and
https://xxx.xxx.xxx.xxx/ is how we have been able to access our VVX500 phones for resetting what provisioning server the phones will point to at RingCentral
I noticed after some firmware update some months ago I could no longer reach the web interface on my VVX410 via http. https does work for me though. Maybe try again and clear cache, etc since it needs you to accept a certificate to connect.
06-23-2017 UPDATED INFORMATION Each Polycom VVX500 which has the RingCentral updated firmware in it
now has a unique password for web access to the handset hardware. Note this is different than before when all handsets shared a single Administrative access password (default from factory is 456) but once the firmware has been updated on the RingCentral system, the password changes to a unique password for ***each*** handset. You can contact your Customer Success Manager or RingCentral Support for the password to the device you are trying to "access via the web browser" - make sure to have the device Serial # (Mac Address) handy when you contact them - this is how they know which associated device password to give you.