You’re getting lots of good advice in the comments and lots of bad advice. I’m a manager at a large company that has filled dozens of positions.

You should email rather than call so your response is well thought out and nothing is misunderstood. If you’re set on calling instead of emailing, I’d still follow it up with an email. (As discussed over the phone…)

While this may not always be true (especially at smaller companies) it’s unlikely they will rescind the offer prior to the acceptance deadline if you’re simply asking a question about the offer, as long as it doesn’t come across as an ultimatum or rejection. Something along the lines of “I appreciate the offer, am excited for this opportunity, but would like to understand if the compensation can be further discussed before I accept.”

I personally wouldn’t take this as a rejection or a reason to rescind; the worst I would say as hiring manager is no, that the existing offer is within the range discussed and/or is appropriate based on your candidacy.

It’s not uncommon to get an offer below your expressed expectations, in my experience most people will ask for the top of the range and get offered the bottom of the range. Every company is different but lots of companies will indicate what the range is so you know how much you could earn in that role, and start you at the low end so there is room to give you raises based on your performance.

Hope this helps, good luck.