German phrase
Unter welcher ~ dürfen wir Sie kontaktieren?
Meaning
Which ___ should we use to contact you
When to use it
It asks how to reach someone. A polite choice for professional communication.
Example dialogue
Unter welcher Telefonnummer dürfen wir Sie kontaktieren?
Which phone number should we use to contact you?
Am besten erreichen Sie mich telefonisch.
The best way to reach me is by phone.