How to add "Phone no" to the "publish your add" form filling section of bender

[bernascoginger]

hey buddies,
 
I am an amateur in programming, but i have successfully installed the osclass open classifiied software.
I want to edit the "Publish your ad" form to include "Phone no:" .

 I want my users(publishers or sellers) to be able to add their phone numbers to their items posted so that they can be contacted directly by buyers.
Please can any body help me edit the bender theme to include "phone no:"

[Heartcore]

use custom field dude...