Hey @OPopp,
when I get you right you just want to know a better/safer/more elegant way to store the data provided by your form?
It really depends on what you want to do with the stored data. If you just want to save it - CSV is fine I guess.
If you want to work with the data later on I would think about storing the data in a json-file and give every data an id of e.g. a timestamp. So you can easy work with it in each language (js, php) and you dont have to create arrays from csv files later or so.