If you have a free developer account then you need to redeploy the app to your phone every 7 days. You can only add up to 3 devices to your free account, and there's no way to remove them without paying (at least that I could see when I let my subscription lapse), so good luck if you replace your phone too many times or try to share an app with a family member or friend.

It's not impossible, and perhaps it's easy if you've already hit all the pitfalls and know where they are, but I would not describe it as easy.