(If I got you) You need something like this:
public static void Main()
{
String inputname, inputphoneno, userselection;
String[,] addrbook = new string[20, 2];
int n = 0;
do
{
Console.WriteLine("Please select and option" +
Environment.NewLine + "1. Add Entry" +
Environment.NewLine + "2. Delete Entry" +
Environment.NewLine + "3. Print Book to Screen" +
Environment.NewLine + "4. Quit");
userselection = Console.ReadLine();
switch (userselection)
{
case "1":
Console.WriteLine("Name:");
addrbook[n,0] = Console.ReadLine();
Console.WriteLine("Phone No.:");
addrbook[n,1] = Console.ReadLine();
break;
case "2":
break;
case "3":
break;
case "4":
break;
}
n++;
} while (userselection != "4");
}