Yes, I am very sure. There is no iPhone where it is possible to upgrade the storage after purchase.
See the following from About storage on your device and in iCloud - Apple Support
When you buy your iPhone, iPad, or iPod touch, it comes with a set storage capacity ranging from 16 to 512GB for iPhone, 16GB to 1TB for iPad, and 8 to 256GB for iPod touch. The music you buy, the apps you download, the photos you take, and all of the other content that you enjoy on your device uses its storage. And depending on the size of your capacity and how much content you have, your device can fill up and run out of storage. When your device is full, you can’t increase its storage. But you can free up space.
There are some other things in that article that may help.