Yes, you can search by image on iPhone. There are a few different ways to do this.
One way is to use the Google app. When you have the Google app open, tap on the camera icon in the search bar. You can then either take a photo or upload one from your camera roll. Once you've done that, tap on the magnifying glass icon to perform a search.
Another way to search by image is to use the Safari browser. Go to the image that you want to search and tap and hold on it. A menu will pop up giving you the option to "Search Google for This Image." Tap on that and Safari will perform a search.
You can also search by image using the Photos app. Just open the app, go to the image that you want to search, and tap on the share icon in the bottom left corner. Scroll through the options until you see "Search Google." Tap on that and a search will be performed.