Thanks for using BigContact.
We have been experimenting with the current form design since 2007, and we have found that making a phone number a required field decreases contact form conversion rate.
However under current plugin license you are able to modify the code as you wish.
For the pattern part, we are releasing another update that removes the pattern and placeholder for the phone field, as the phone format might be different for international users. Currently this is around line 56 of file
As far as making the phone field required, you could add a required attribute to the phone input form on the same above file, and add some validation for it in
You might also want to keep your settings page in harmony with your changes by removing the optional text from phone input field in admin
I hope this helps, and please rate us a 5Star