Images can be sized according to pixels, or percentages. With pixels, the image is a fixed size. When viewed on a phone or tablet, the image will be shown in full, but the text in Web Presence Display Messages may be very small, and require zooming in.
With percentage, the image scales based on screen size - from a smartphone to a desktop computer, text is readable, and the image is appropriately-sized.
To have images scale based on screen size, after inserting an image, highlight the image > Insert/edit Image. Dimensions should be between 1% and 100% - use the same percentage in both dimension fields.
After adjusting, view the web page on a desktop/laptop and a smartphone, to be sure it looks right on both. Edit the dimensions, if needed.