How do you have the column defined? Which iPhone are you testing on?
If you tap the “+*#” in lower left, do you see the decimal separator then?
There are settings within the device to customize keyboards. Nothing jumped out at me that would control the type of keyboard shown.
I have an iPhone 7 and tested Number, Decimal and Price fields in an app. I get this keyboard below. I haven’t needed to do anything to make that happen.
