When I tap and hold on an app icon on my iPhone to uninstall it, the ⓧ button do not appear for certain apps. As far as I recall, the apps in question were installed using a different Apple ID which I have since removed from my iPhone.
I also tried uninstalling by going to Settings app → General → iPhone Storage → App Name, but couldn't find the Delete App option even there.
This is a company owned iPhone 5s running iOS 12.3.1. The device remotely managed. The apps in question are not managed and were installed using a personal ID.