Antifreeze and phosphate

[David Conner <conner@ra.cfm.ohio-state.edu>]

Audi says to use antifreeze that contains NO phosphate.
How can you tell if antifreeze has phosphate in it.  
Prestone lists the ingredients and phosphate isn't one of them.  
But Prestone has another more expensive type of antifreeze
that states in large lettering "Contains No Phosphates".
Does this imply that the less expensive variety isn't safe 
to use in the Audi?  
What harm will phosphate do?

David Conner
conner@cfm.ohio-state.edu
87 5000S
89 100E