Phrasal verb: Step up

To step up is to do what needs to be done, especially in a difficult moment.
It can mean to make an extra effort, to take responsibility, or to show courage, depending on the context.
As with most phrasal verbs, step up is an informal way to express this concept, so you would be likely to hear it in conversation, or see it in a blog post or email that has an informal style. Here are a few examples:

You: I was impressed by the way that John stepped up in the meeting, weren't you?
Your colleague: Yeah, especially when he defended Patty. That was great!

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Your boss: This is an important project, and we need everyone to step up. I'm counting on you to meet the deadline with excellent results.

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Dear Bob,

I'm writing to thank you and your team for stepping up and delivering a great campaign. Everyone did a wonderful job and the results so far are very good. Please let the others know how much we appreciate the extra effort and great teamwork.

All best,

Joshua

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The verb here, step, is regular. Step up, stepped up, stepping up, etc.