Using A Variable For A Column Name In A Query

Is it possible to use a column name variable in a Select Statement for a column name?
For example I have a dropdown with FName,LName,Phone and a text box. The user can select the field to search and the criteria will go into the text box. The problem is the select doesn't like a variable for the field name. I have tried both a standard variable and a Case statement (see below). This is being used in a Stored Procedure with MSSQL. The actual select is much more complicated than this but it gets the point across.
Thanks for your help in advance
@Field as varchar( 50),
@Value as varchar (50)
SELECT *
FROM customers
WHERE @Field = @Value
OR
SELECT *
FROM customers
WHERE
     CASE WHEN @Field = 'Fname' THEN Fname = @Value END,
     CASE WHEN @Field  = 'Lname' THEN Lname = @Value END,
     CASE WHEN @Field  = 'Phone' THEN Phone = @Value END;