In October 2020, Apple rolled out an iOS update that discontinued and removed the TV Remote app from the App Store. This wasn't a huge deal, but it did change the way you could control your Apple TV with your iPhone (if you didn't want to use the Apple TV remote). Instead of accessing the Remote app, you now can access the Remote feature via your iPhone's Control Center.
Here's what you need to know.
How to control your Apple TV from your iPhone
The Remote feature has been integrated into the Control Center on all iPhones running iOS 12 or later. You can access the Control Center by swiping down from the upper-right corner of your iPhone (this applies to any iPhone with a notch). If you have an older iPhone with a Home Button (meaning no notch), you can access the Control Center by swiping up from the bottom of the screen.
Once in the Control Center, you'll see the icon for Apple TV Remote. If you don't see it, you can turn it on by going into Settings, then Control Center and enabling it if you already turned it off. It works exactly the same as the TV Remote app, so there shouldn't be a learning curve. You just have to remember that you look for this remote control feature in a different place.
Alternatively, treat yourself to the new-and-improved remote
Of course, you can still use the Siri Remote to control your Apple TV, which is probably the easiest option for most people. Apple released a redesigned version of the Siri Remote with the latest Apple TV 4K, and the new remote is thicker and less symmetrical, so it's more comfortable to hold and easier to use in the dark.
You can purchase the new remote and it'll work with your older Apple TV, too. If you're looking for a different option, Apple lets you use an Xbox or PlayStation wireless gaming controller as an Apple TV remote (here's how).