Switching beetween Editors and zooming text during presentations or so could be complicated.
If you used to do it like in notepad++ than maybe this helps if you use win:
The pre-defined schemes are not editable. To change colors and fonts settings in such a scheme, create its copy.
So to change font size select any scheme of your choice. Save the "scheme" as a copy with a name like "scheme 2".
Now the default font size will be editable.
In MacOS, you should navigate to the PhpStorm -> Preferences -> Editor -> General screen and check/uncheck the "Change font size (Zoom) with Command + Mouse Wheel" checkbox. I unchecked because I don't like it but maybe you do.
Moreover, you can use the finder field in the top left corner of the same PhpStorm -> Preferences dialog. Type the word "size" in this field and you will see a couple of items on the right hand side of the dialog. There are the Editor Actions -> Decrease Font Size and Editor Actions -> Increase Font Size options.
Right click each of them and choose "Add Keyboard Shortcut". Finally, press the Ctrl and numerical plus in case of Increase and Ctrl and numerical minus in case of Decrease and press OK (if you have numerical part of your keyboard).