You should be able to ping your Apple Watch from your iPhone.
Can't find your iPhone? The Apple Watch lets you ping it — press one button on your Watch and your iPhone will play a loud, sonar-like sound, just once, to help you find it.
I use this feature all the time, as my iPhone routinely gets stuck between couch cushions, or goes missing somewhere in my apartment.
It would be great if the iPhone had this feature, too, where you can ping other Apple devices, like your Watch, in order to find them. (You can only ping AirPods from the iPhone, as far as I know.)
The iPhone should have Theater Mode, one of the Apple Watch's best features.
On the Apple Watch, pressing the comedy/drama symbol in the Control Center activates "Theater Mode."
Theater Mode automatically silences your Apple Watch. It also prevents the screen from turning on unless you tap it.
The iPhone has a convenient mute switch, but it's not as all-encompassing like Theater Mode, which also makes sure your iPhone doesn't accidentally light up a dark room (like if you're watching a movie, or sitting through a PowerPoint presentation at work).
The iPhone should give you motivational texts and badges like the Apple Watch does.
I love how the Apple Watch constantly rewards you throughout the day — particularly when it comes to exercise.
The iPhone could do this, too. Maybe it doesn't reward you for movement, but perhaps it can reward you for limiting your screentime with your phone, or certain applications, through Apple's new Screen Time feature.
Or maybe it could reward you for trying new apps in the App Store, or not snoozing your alarm repetitively every morning.
The iPhone's Weather widget should show you more information at a glance, like the Apple Watch can.
By simply lifting the Apple Watch, you can see all sorts of weather details: the current temperature and range throughout the day, the chance of precipitation, the UV index, and the wind speed.
You can also get a 10-day forecast by clicking on the Weather complication from your watch face.
On the iPhone, turning the screen on and swiping to the left can let you see weather at a glance (if you've activated the Weather widget). But the information is pretty basic: It will give you the current weather, chance of precipitation, and a five-day forecast. I'd love to be able to get more weather details at a glance, but have them also appear directly on my lock screen, instead of on this second page of widgets.
That brings me to my final point ...
You should be able to customize your lock screen like you can on the Apple Watch.
Save for the wallpaper, everyone's iPhone looks exactly the same.
The iPhone features the time and date towards the top center of the screen, plus a few details like signal strength and battery life, and a couple of controls like quick access to the flashlight and camera.
Given how long the iPhone has been in existence, it's surprising to see how the lock screen hasn't evolved at all.
The Apple Watch's "home screen" is way more customizable.
Unlike the iPhone, it's very possible that no two people will have the same Apple Watch face.
With the Apple Watch, you can choose from an array of watch face styles, which effectively changes how your home screen looks. Some of them are static, but many of them are animated, which makes me wish the iPhone had more animated wallpaper options.
You can choose to have the time take up the entire screen, or hide it in a corner somewhere. You can choose to hide the date entirely. You can change the color of your text. You can add a ton of quick-access controls for things like messaging, timers, and your calendar.
You can't do any of this on an iPhone. But you should be able to.