Internet Connection: Phone to PC. And back?

[WWGD]

Hi all,
Hope this is not a " where do I buy the latest version of the interweb " question. How does one send a file
from a PC ( win 8.1 ) to a smart phone, knowing only the phone number? What info do I need in order to send it?
Thanks.

EDIT: Never mind, DUH. If I received a file in my email service, I can just attach one and send it back
to the same address. If mods prefer, I can just delete it.

 

[StevieTNZ]

If both devices have bluetooth, you could have used that.