Font Size: Problems with changing the presets

After publishing my post, I felt that the font size on my phone was too small.

So I went back to the post, opened the page/block settings, changed the font size for each text element (except the headings) to size M.

As this M size was a little too big, I thought that changing the global settings would help.

So in Appearance > Editor > Styles > Typography > Font Size > M, I fiddled with the rem. I increased it from 1.25rem to 1.3rem and higher but that made no difference to the font size on my phone.

In the end, I switched the preset size M back to the original size 1.25rem. The text on my phone now looks too small again even though on the page/block settings, the M is still selected.

Could you guide me on how to change the default font sizes, especially for mobile view?

The page I need help with: [log in to see the link]