Pass API correct attribute to search inbound SMS
Pass API correct attribute to search inbound SMS

It’s `phone_number` here:
https://github.com/alphagov/notifications-api/blob/1250e47cc7c34356f33079a7490c8e548ebd0f3f/app/inbound_sms/rest.py#L33
alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin