Depending on my view, I frequently want to change the font size, but the existing solution (ctrl+=) zooms the entire interface. There is no solution to bind a keyboard shortcut to zoom the font, but a slider in the settings exists, so it is possible.
Simply add the keyboard shortcuts/hotkeys Increase font size, and Decrease font size.
I love Obsidian, the best markdown/text editor ever! 
(I know you can use the mouse wheel, but I want to be able to use the keyboard too).
No response? Weird… I think this is important. I like my overall system zoom; sometimes I just need the text I’m reading to change size. I’m not trying to zoom everything.
For the record, using Ctrl + Scroll Up/Down will do the behavior you (and I) are looking for, but it’s really sensitive and I’d prefer a keyboard shortcut so that I could “step” the zoom level, the same as you do with System Zoom.
I am shocked that this does not have more votes. It’s infuriating that I can only use the keyboard to change the zoom level and there isn’t even an option to add a shortcut to change the font size. This really feels like an oversight on by the Obsidian team, so it’s disappointing that there’s no reply here.
I change the font size multiple times per day, as I sometimes need text to be a bit bigger if someone else needs to read along. It would probably become one of my most used keyboard shortcuts.