You would create external .php file(s) with your function definition(s) and require it/them when needed. If you use OOP classes, you can set up an autoloader so that definitions are loaded as needed. Note: OOP class(es) are NOT collections of unrelated functions/methods. Don’t simply lump all your functions into one class. The functions/methods in any particular class should be related to the purpose/name of the class they are part of.
The name you give a function should indicate what processing the function does. There would be no need to rename a function unless you change what the function does and if you are regularly editing the code inside a function, it’s a sign that the function is not general purpose and instead of doing something reusable, has the wrong responsibility and probably contains part of your main application code.
Functions should receive all input(s) as call-time parameters and return the result of their processing to the calling code.
If the above doesn’t seem to address what you are doing, you will need to post your function definition(s) and usage.
