The most effective phone calls take less than a minute: say your name, your city or ZIP code, and what you support/oppose, maybe a sentence on why. You’ll be marked down on a spread sheet that is discussed at the daily office strategy meeting.
Other actions like brief emails, meeting in-person at the district office, meeting in-person at the DC office, can also be effective, but take more time and energy. Emails aren’t always read right away like a phone call must be answered for example. And you generally need to make an appointment for an in-person meeting.
See also: Atlanta city council voting for Cop City despite over two hundred people showing up at the meeting, in person, to speak against it. (Not to mention a petition for a referendum that got hundreds of thousands of signatures but was illegally withheld from the ballot anyway.)
You’re right that actually talking to your representatives works surprisingly often, but sometimes it really blatantly doesn’t.