Yes, if you purchase for iPadOS through either the Apple App Store or the Mac App Store, you can also install that on your iPhone (or any other Apple device you have). One thing to keep in mind when working with both app stores is that you could run into an issue where it acts like it's going to charge you a second time. If you proceed with the purchase, it will recognize you've already purchased the app and let you install it without charging you. There is another post on the forum that discussed this if you have any concerns.
Mike
Mike