Display label based on database value

I am trying to set up a phone directory where some people have two phone numbers.  I only want phone2 to display if there is a number in it.  Problem is that the database field has  either a null value, a value of --, or a legit number such as 1234567890. 
If the db value is null or "--", I do not want to display anything.
If there is a number it should display "or 123456789".   I'll also need to format, just not sure where to use something like:
string.Format("{0}.{1}.{2}", dr["phone2"])
Here's my code for the phone2 field. 
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