This expression looks really complicated, but it's easier to understand with a few examples:
It's hotter in Washington than it is in Los Angeles.
She's happier in the new apartment than she was in the old one.
English speakers often phrase comparisons differently:
Bethany is a lot quieter in person than over the phone.
It's hotter in Washington than Los Angeles.
But this is technically wrong. It can lead to confusion sometimes:
John's better friends with Ben than Stacy.
Does this mean that John & Ben are closer than John& Stacy? Or does it mean John & Ben are closer than Ben & Stacy? It's unclear. So it's better to say:
John's better friends with Ben than he is with Stacy.