Since the evaluation order is as follows:
you can omit the brackets:
{% if not owner.home_number or owner.work_number or owner.mobile_number %}
No contact number available
{% endif %}
Or, just FYI, you can also cancel the check:
{% if owner.home_number or owner.work_number or owner.mobile_number %}
{% else %}
No contact number available
{% endif %}
source
share