It is helpful when posting questions to include details like versions. What outlook version are you using? Also is this a company-wide change you want to make or just for your pc?
As technochic’s response is accurate, there is a basic way to do what you are requesting which should work from Outlook 2000 and on. This method will actually effects all windows, but it gets the job done: go to your desktop, right click, select properties, select appearance, select font size. If you increase the font size, this will change text in window titles, and stuff like the outlook side pane and folder list. You can click advanced to change specific attributes and taylor the settings to what you want.