With Bootstrap 4 you have to design for the phone first and then for the bigger devices.
If you first develop for desktop and then for phone the order of bootstrap seems a bit strange, if you want to have a different style just for phone and and other for all other devices, then you have to set the phone style on the All property and the style for all the other devices on the phone property.
For someone that doesn’t know how the order in bootstrap is, that can be very confusing. I think the All property is clear enough, but for the others it should probably say like for tablet deveice and up, now users unknown with bootstrap would probably think they set a style specific for tablet when they select it. Or perhaps highlight all the devices that are being affected by the change.
I hope you guys can give us some good feedback on this.