"Do you have my phone number?"
Translation:¿Tienes mi número de teléfono?
I believe that "de" is used in thus circumstance to represent "of".
In Spanish, there are no possessive suffixes such as English has.
For example, in English, I would say "The woman's candy" where the " 's " is the possessive suffix. In Spanish however, I would say "El dulce de la mujer" meaning verbatum "The candy of the woman"
Does that make sense?
Hope that helps!