Why won't the iphone allow making calendar appointments from contacts app?
This is pretty basic and should be added to the iphone IOS. Go to a contact, create an appointment to call the contact.
Telling other users in this user-to-user technical support forum will not get Apple's attention. Use http://apple.com/feedback.
You can use Reminders instead of the calendar. Just hold the HOME button and say to Siri "Create a reminder to call John Doe tomorrow at 4 PM". The reminder will have an icon to call the contact's number.