Final answer:
The Phone Company needs to purchase 8 core licenses for Team Foundation Server 2018, considering their server has four dual-core processors.
Step-by-step explanation:
The Phone Company wishes to run Visual Studio Team Foundation Server 2018 on two virtual machines that will reside on a server with four processors, each with dual-cores. According to the licensing requirements for Team Foundation Server 2018, a user needs to license each processor core in the server. Therefore, since the server has four processors with two cores each, the Phone Company would need to license a total of 8 cores.
In order to run Visual Studio Team Foundation Server 2018 in two virtual machines on a four-processor dual-core server, the Phone Company should assign two licenses to the server. Each virtual machine would require a separate license, so with two virtual machines, two licenses are needed.