This is the best phone mount you can get for your 1996-2001 Audi A4. We use these mounts in our own cars, they're simply the best you can get. Use with any phone, simply stick magnet to the back of your phone or case, or slip the metal between your phone and case. Includes instructions.
Video showing installation: https://www.youtube.com/watch?v=eqrrBawngKs&feature=emb_imp_woyt
Fitment: