multiple RingCentral accounts on same phone

are you talking about a DECT phone?
For example a base station with 2 handsets and have each handset assigned to a user extension belonging to a different account?
Although I have never done it, you might be able to get it to work by setting up the 2nd ext. via manual provisioning. I recently explained how to do this here:
https://community.ringcentral.com/questions/114249/yealink-w79p-with-two-handsets-and-different-exten.html

The only difference in your case is that you would be getting the SIP details from a different RC account to set up the "Account2" on the phone.