What's the best way to join on the same table twice?

First, I would try and refactor these tables to get away from using phone numbers as natural keys. I am not a fan of natural keys and this is a great example why. Natural keys, especially things like phone numbers, can change and frequently so. Updating your database when that change happens will be a HUGE, error-prone headache. *

Method 1 as you describe it is your best bet though. It looks a bit terse due to the naming scheme and the short aliases but... aliasing is your friend when it comes to joining the same table multiple times or using subqueries etc.

I would just clean things up a bit:

SELECT t.PhoneNumber1, t.PhoneNumber2, 
   t1.SomeOtherFieldForPhone1, t2.someOtherFieldForPhone2
FROM Table1 t
JOIN Table2 t1 ON t1.PhoneNumber = t.PhoneNumber1
JOIN Table2 t2 ON t2.PhoneNumber = t.PhoneNumber2

What i did:

• No need to specify INNER - it's implied by the fact that you don't specify LEFT or RIGHT
• Don't n-suffix your primary lookup table
• N-Suffix the table aliases that you will use multiple times to make it obvious

*One way DBAs avoid the headaches of updating natural keys is to not specify primary keys and foreign key constraints which further compounds the issues with poor db design. I've actually seen this more often than not.

The first is good unless either Phone1 or (more likely) phone2 can be null. In that case you want to use a Left join instead of an inner join.

It is usually a bad sign when you have a table with two phone number fields. Usually this means your database design is flawed.

You could use UNION to combine two joins:

SELECT Table1.PhoneNumber1 as PhoneNumber, Table2.SomeOtherField as OtherField
  FROM Table1
  JOIN Table2
    ON Table1.PhoneNumber1 = Table2.PhoneNumber
 UNION
SELECT Table1.PhoneNumber2 as PhoneNumber, Table2.SomeOtherField as OtherField
  FROM Table1
  JOIN Table2
    ON Table1.PhoneNumber2 = Table2.PhoneNumber