Here's the answer:
“其实那个更大”
(qíshí nàgè gèng dà)
Watch a real native speaker say it:
Here's how it sounds in a textbook:
You could also say:
- qíshínàgègèngdà
- qíshí nàgè gèngdà
Fun fact: the hundreds of thousands of people learning Chinese with Memrise get this phrase correct 98.08% of the time!