Hello,My question is are you planning in the next versions of KUIB to add a suitable resolution for phones. Currently there are added options for desktop, laptop, 2 for tablets.
Kendo UI Builder is focused on developing complex business applications for browser form factors. Usually the features of a mobile app do not match the workflow of large system of records built using KUIB (or other development platforms) so even if the screens were responsive there would be a lot of differences and how that affected the workflow would need to be considered. You can use Telerik Platform for your mobile app development and leverage the same business entities as KUIB.