How can I get more iPhone space

You can’t get more space. The amount of space the device has when you purchase it, that is the amount that device is always going to have. Apple devices do not have upgradeable memory and they cannot use memory cards to help increase their size. It’s always best to plan ahead and get more space then you will need when you get your phone so you don’t have to worry about running out of space. You cannot get more memory later

Delete things from the device.