If the called or calling phone number is not associated with a supported Salesforce object, calls will typically display as "Unknown" in the communication panel, and there will be no tab or window pop.
Verify that the phone number involved is assigned to a standard, supported Salesforce object. It must be correctly listed in a phone number field.
Only the following Salesforce objects are supported:
Note: FAX phone fields are not supported by the integration in any Salesforce object.
It's possible the supported Salesforce object has been disabled for search. In the communication panel Setup, search for supported Salesforce objects must be enabled
If a phone number exists only in Salesforce objects (such as Contacts) that search has been disabled for, no screen pop will occur for that number.
Salesforce objects supported for search by both old and new 8x8 Virtual Office integrations are:
In the older communication panel (left), the search options are found in the Settings (gear icon) / Search Object Type
In the newest communication panel (right), these options are found in More / Settings / CRM Objects to search
It's possible that phone numbers in Salesforce are assigned to a Person Account. Person Accounts are a rare type of Salesforce object that have been converted from Contacts by Salesforce itself, at customer request.
Salesforce Person Accounts are not (and will not be) supported by the 8x8 Salesforce integration, and will not pop records on inbound or outbound phone calls.
If the Salesforce Phone fields in a supported object (such as Contacts) have been significantly customized, phone numbers for inbound and outbound calls could fail to be recognized by the 8x8 integration, and will not pop a tab or window.
Changes like this are made by a Salesforce administrator/developer, and cannot be resolved by an end user without Salesforce Administrator role access.
Note that simply re-naming the Phone field label does not normally break this function.