The IP address assigned to a server is listed right on that server’s detail page. Open the server from Services > Servers: its primary IP Address (and IPv6 address, if it has one) appears near the top, and the Network Interfaces section lists each interface’s IPv4 address, gateway, and netmask.
You don’t have to assign one yourself, either. When you deploy a new server, Phoenix assigns an IP automatically; if you have reserved IP blocks, you can pick which address to use during configuration.