Linking anonymously two phone

I'm looking for a solution (API) that would allow me to have on my website a button that, giving to phone numbers, would:

1. put in relation two people (over their phones)
2. keep both interlocutors anonymous to each other

I've seen some offers but they all contain other services I'm not looking for. I'm also looking for any keywords that would help me searching for such an API (from what I've understood so far it seems to be called Request-a-Call).