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.
Best Answer
Screen Time settings were preventing the app from being uninstalled from my iPhone. The setting can be found by going to Settings app → Screen Time → Content & Privacy Restrictions → iTunes & App Store Purchases → Deleting Apps. The setting was set to Don't Allow.
As soon as the setting was changed to Allow (default value), I was able to uninstall apps normally and the ⓧ button appeared on the app icons when I tap and hold my finger.
When uninstalling an iPhone app, it doesn't matter if it was installed using the currently logged in Apple ID or using an Apple ID that has since been removed from the iPhone.