I received a job inquiry email from an HR person, now what?

I just don't want to make a mistake here, but this situation is driving me crazy, here are the details:

I received a job inquiry email from an HR recruiter at a large company on Monday 04/22 requesting to talk via phone about a job opening at their company. I responded that I was interested via email and haven't heard anything in 4 days. The recruiter included his phone number in the email signature, is it appropriate to call the HR recruiter and when? Man this feels like online dating or something haha!

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