That all depends....
If the provider does not send a name, then all you can do is to enter the number and a name in the 3CX phone directory. That will display any name you wish if there is a number match. You can also change a name that is being sent to something more meaningful, such as "Mobile Caller", to a persons actual name. Of course this only works for frequent callers that you go to the trouble of putting in there.
Some providers, depending on the country/policy, do offer a name display service, but charge extra, as a name lookup in a database generally has a fee.
Check the 3CX logs for an incoming call, to be sure that a name is not being sent.