I was told to ask this question here. There’s a saying in writing to “show; don’t tell”. For example, instead of naming the emotion, “She was angry”, you would show the emotions happening by saying, “Steam started coming out of her ears,” or “Her fists slowly clenched up.”
I am looking for a “showing” phrase for being nervous. The only one I could think of was: “Her heart was pounding heavily.”
Showing instead of telling means showing the consequences of a character state (anger, anxiety, love, worry, hate, etc.) instead of labeling the state.
"Steam coming out of her ears" is a cliché, originally intended as the consequences of a metaphor for the heat of anger, itself not necessarily literal, but a reference to flushed skin causing a redder appearance.
What do people that are nervous do? They may shake, stumble over words, be clumsy, and spill something. They are often anxious about the outcome of what they are doing, like blowing a job interview. They may make inappropriate comments or jokes, trying to be funny and alleviate the tension that only they really feel. The tension and worry they DO feel may be distracting and cause them to make mental mistakes: Call their interviewer by the wrong name, for example, or blank on a rehearsed reply to an interview question.
Or, if they are making a presentation, get flummoxed by an unfamiliar projector or piece of computer equipment, or a clicker for the slide projector that doesn't seem to work as they expected, or speaking too closely into a microphone and startling themselves with the result. They may blush at their mistakes. They may sweat.
There are many possible consequences to being nervous, pick a few, and use them. Or use the general idea (distraction and worry) and come up with an original ramification for it: a consequence, an implication. Describe something visible or tangible.
"Show don't tell" doesn't mean that for every feeling there is a periphrasis that expresses it better. So there is not a specific phrase to use for each case. It's never about single expressions, but rather about actions.
"Her heart was pounding" is ok, but it's not enough: you want to express a condition throughout the whole scene, so one single phrase is not the solution (in most case, I mean). For example, you need to "show" someone nervous, not try to find a fancy way to express nervousness. Your character needs to do actions that are dictated by that feeling. "She was tapping her feet rapidly" or "she couldn't stop bite her fingernails with her teeth".
Since people have already posted answers about the general "show don't tell" method I'll try to put the focus more on a specific answer for your problem.
I'd say start with thinking about your character. So she or he is nervous. How would they act? Would they start fidgeting? Maybe try giving a glimpse into their thoughts: the questions that are running through their mind.
I personally (but this is just me and my weirdness) would research what ticks people show when they get nervous and pick one or two that suit your character.
I hope this helps.
