Why is query with phone = N'1234' slower than phone = '1234'?

Question

I have a field which is a varchar(20)

When this query is executed, it is fast (Uses index seek):

SELECT * FROM [dbo].[phone] WHERE phone = \'5554474477\'         


        

Answer 1

 SELECT * FROM [dbo].[phone] WHERE phone = N'5554474477'

is interpreted as

 SELECT * from [dbo].[phone] WHERE CAST(phone as NVARCHAR) = N'5554474477'

which prevents index usage