In a professional context, when calling individuals who do not answer, you might describe the situation as follows:
"I attempted to reach out to [Name/Department] via phone to discuss [specific topic or purpose]. Unfortunately, I was unable to connect with them as there was no response. I will continue to follow up via email or consider alternative methods of communication to ensure that the matter is addressed promptly."
This description maintains a professional tone and shows initiative in seeking alternative communication methods.