curl --request GET \
  --url http://localhost:8080/api/phone-numbers/{phoneNumber}/exists \
  --header 'X-API-KEY: <api-key>' \
  --header 'X-API-SECRET: <api-key>'

{
  "message": "Phone number existence checked successfully",
  "status": "success",
  "error": null,
  "data": {
    "organization_id": "org_123",
    "phone_number": "+14157774444",
    "exists": true
  }
}