Get-DHCPServer cmdlet in Windows 2012R2 Server

DHCP Server Cmdlets in Windows PowerShell

The GET-DHCPServer cmdlets get automatically installed if the DHCP Feature is installed in your Windows 2012R2 Server

But if you are using the Windows 2012 R2 Server as a member server and your DHCP is running on either a Windows 2003 / Windows 2008 Server you will need to install the Remote Server Administration tool instead

Just run below command to get the cmdlets

Install-WindowsFeature -Name RSAT-DHCP