OK, am a little confused.
You have 2 accounts with Nexvortex? The question you posed earlier indicated 2 DID which is not necessarily the same.
You can have one account with Nexvortex and that one account can have any number of DIDs. Of course, you can also have multiple accounts with nexVortex and again have any number of DIDs on either, all, etc.
The phones have nothing directly to do with the account, but rather, you set up extensions and then with the outbound rules establish how the call will be routed and whose account will be affected and how the caller-id will be presented.
There are a couple of ways:
1. If one account, set up the phones with extensions that represent the various companies (ext 100 - 300 for company A & 400 - 700 for company B as an example). In the extension attributes, set the caller-id for company A on their representative extensions and similarly company B for their associated extensions. There would only need to be one outbound rule as it pertains to nexVortex (more rules may be needed for specific dial plans, but they all cumliminate with using the one nexVortex account), and you could use the reporting feature of 3CX to tally the minutes made by each company's extensions if cost allocations are needed.
2. Do the same as above, but if multiple accounts, then set outbound rules based upon the extension and point to the nexVortex account (port) of interest for Company A and again to the port of interest for Company B. This eliminates the monthend tally and allocation.
In either case, it will be incumbent upon the user to select the proper extension to enure that the propoer company caller-id is being presented as well as for cost accounting purposes (if needed).