You just import them into the project and align it again. If it won’t align, then you will need to use some control points to align those images. Of course, you can use also your iPhone images, I think it would be even better than from Google.
You can turn off georeferencing for these images and keep just georeferencig from first images.
There is a tutorial about merging different components, which could be helpful in your case: https://www.youtube.com/watch?v=rrXuHcqoOjQ&t=419s. The principles are still the same.