When creating an individual record, how do I make the phone number field a mandatory field. I mean, I don't want a record before the phone number is written.
I assume you are wanting to require a phone number when some contributes, becomes a member, or registers for an event.
Go to Admin > Custom Data > Profiles
Look for the Profile that you will be using in your Event/Contribution pages and to the right click Fields
You can edit the Phone field and make it Required