OK, so I cropped each of the original images to a square and sized each down to 1000 px x 1000 px and each ended up being 1.64 in x 1.64 in and 240 px/cm. From Photoshop, each image was identically sized.
I replaced them on my website and from a laptop, the page looks fantastic and each image is identically sized. But unfortunately, it still is wonky on my iPhone. Here, the first images in each row (Welcome, About Me) is one size, the second images (People, Blog) are another, the third (Nonprofits, Investment) are larger than the first two, and the fourth (Small Businesses, Say Hi) are another size entirely.
I'm not sure what I'm doing wrong. This time, I even removed the original images and gave the 1000 px x 1000 px images original names so that there would be no confusion within WordPress.
Sigh. Any advice would be greatly appreciated.
One thing just occurred to me while viewing it on the iPhone. Would the wonky image sizing have anything to do with the amount of copy appearing beneath each image? The image sizes strangely seem to coincide with how much copy is beneath them.