Interrapt G26

Description
The phone field in the Attendees menu should accept minimum 5 and a maximum 15 numbers. User are allowed to created attendee with phone number who can contains less than 5 and more than 15 digits.

Steps to reproduce:
1. Login on interrapt
2. Click on Attendee from the sidebar
3. Click on create
4. On the phone filed eneter:
- phone number with less than 3 digits
- Phone number with more than 15 digits
5. Fill out all other fields
6. Click on create

Expected result
New attendee should not be created, message in red letters should be shown that the phone field is required. The criteria for the phone is number with more than 3 digits, and less than 15.
Actual result
New attendee is created. The phone filed accepts numbers with less than 5 characters, more than 15.