In a largely object-oriented world, one Redditer asks if it's still okay to just use functions, the more procedural method of PHP development:

Is there anything wrong with using an include file of functions instead of using full code in a file? [...] Obviously you wouldn't write functions for one off tiny things, but I think it would help to read files altogether especially if the functions file was alphabetically listed.

There's several suggestions in the comments including things like:

• You should also look into using a templating engine, so you can separate your html from your php code.
• One thing you could always ask yourself is "Do I will ever need to write that part a second time somewhere else ?" If "yes", that means you should put that part in a function.
• Before you go writing a load of functions and putting them all in a file, which can get quite unmanageable, consider grouping them logically and placing them in classes.
• Function names should start with a verb though (except for trivial getters whose meaning is clear by context, which can be named after the thing they get).
• Do group them logically, but it's not necessary to place them in a class unless they share data or state.