I'm using the basic theme which is fine for my purpose. However, I find the description very hard to read (font size). Is there method for making the size larger within the Admin configuration? Ironically, the album subject matter is all about accessibility. Using browser zoom isn't option as it's only the text I want to enlarge not the entire page.

Alternate theme would have to be light background, plain.

Go to Options -> Gallery -> Gallery description and use the text field editor options to change the font size of your gallery description.
You must have the tinymce4 plugin activated to get the text field editor in the first place.

I activated the plugin and followed the path you gave. In the Gallery description window, I now see File | Edit | Insert.... but none of those menus offer Font/Size options. I do see option for Header 1-6.

The editor has several configurations you can choose on the plugin's options. Only the "classic" variant has font sizes.

Thanks. Managed to set font size for Gallery title and Subalbum title.

Does this mean I need to format every image description separately? I have close to 100?

If you don't want to modify the theme's css of course.

Will take you up on modifying theme's css. Saw themes > basic > styles > light.css but not sure which controls the description.

The css uses .album p {…} for it as Tinymce adds always a `` wrapper.

As of the theme file itself the css direct chain for the album description would be this:
#albums .album .albumdesc div p { … }.