Sony is probably your best bet -- they still offer microSD card slots, and they're also renowned for their cameras. But they tend to be pretty expensive as well.
Side note -- make sure you're backing up your photos regularly to some kind of reliable storage. SD cards are not considered reliable, and have a finite lifespans. Onboard storage is more reliable, but if something happens to the phone itself (e.g., it gets run over by a truck, or stolen, or the screen breaks, or the motherboard fails), then those photos are gone. I would normally also recommend cloud storage as an option, but since you already said you have 400 GB of photos saved to an SD card, I'm guessing that you don't want to use the cloud.