Other than changing screen resolution or using the "scaled" setting of your display, there really is no way that macOS allows for increasing the font size (text size) of some of its included apps. You might give the TinkerTool app a try to see if that will work. It's a free utility that can be used to change various settings of macOS but sometimes it doesn't work in the way it should.
Thanks for that reminder Charlie. I haven't used that program in quite some time.
The only way I can think of to do this is to make use of the accessibility features in macOS. The Zoom in / Zoom Out features can be triggered from keyboard commands/shortcuts. I've used it for Contacts several times.