"I have called on the phone."
Translation:Yo he llamado por teléfono.
To longtry: Take a look at this site, it explains when and when not to use articles https://www.fluentu.com/blog/spanish/definite-and-indefinite-articles-in-spanish/
To Longtry: When you are talking about things (just stuff in general), you don’t need to use an article if you are talking about the things in a general way, especially if quantity is not important. https://www.realfastspanish.com/grammar/spanish-articles
We may say "on the phone" in English, but it's simply not done in Spanish. The link that @Antonio844159 mentioned talks about this with methods of transportation, but it also applies to methods of communication. This is why we say hablamos por internet and not hablamos por el internet even though in English it's "The Internet". El me envió una carta por correo. He sent me a letter by mail. Or even, Yo recibí un mensaje por paloma. I received a message by pigeon. ;)