Level 75
I'm not familiar with imagejpeg(), but a good package that many laravel folks use is http://image.intervention.io/
It can deal with resizing, etc. But in your question you resize then save.
I suggest practice saving images first before using imagejpeg() just to know how it works.
For a single image I do it this way: https://gist.github.com/jimgwhit/0e4929230cd6b7df4b274b0b04312edd