It really depends what you mean , Virgin Media is a completely separate network, nothing they supply would be used by Openreach ( and thereby BT ) , but , if for example , you had ‘extension’ sockets that you supplied yourself, they would be yours , not Virgin Media, and if you wanted to incorporate them , that would be your choice.
As far as BT , new supply that requires a phone service as well as broadband will almost certainly come with DV ( Digital Voice ) , so the phone plugs into the router …..the router still plugs into an Openreach master socket , unless you live in an area that has access to FTTP , in which case the router plugs into an ONT , fitting that would be part of the installation, and any previous copper pair infrastructure made redundant.
If you were in a copper pair only area , ( not FTTP ) chances are the Openreach master socket should still exist ( especially if in an area served by underground cables ) that is pretty much a fixed point where service will be installed , if in on overhead service area , or an FTTP area fed by underground or overhead , you can ( within reason ) chose where you want the ONT provided
