Reverse phone number lookup was one of the earliest services that Google started providing with search. Today, Google killed the reverse phone number lookup service without putting up any official notice regarding the matter. The service could be accessed with the operator rphonebook: which gives information on the owner of a residential phone number if it is listed. The sister service of looking up other phone numbers that could be accessed using the phonebook: operator is also gone now.
The service used the phonebook directory to lookup this information and present it.
Things change, and Google has dropped the phonebook: and rphonebook: operators for finding phone numbers (rphonebook: was for “residential phonebook” and focused on home phones). As you can imagine, this was an endless source of hassles for people (who were surprised to see themselves searchable on Google) and for Google (who had to constantly deal with all of the takedown requests and outraged letters from folks who thought they were unlisted).
With this service gone from Google, there is another service that lists some similar data. It is explained at this page on SearchEngineLand. Apparently, the reason for Google dropping this service is twofold.
Firstly, there were numerous takedown notices and hassles for people and they wanted to opt out of getting listed. Secondly, the service was losing importance and fewer people were using it. Critical decisions like these are hard to take, and Google has been wise in killing this feature.