Should I mention that I quit my job and give up good salary to take a PhD degree in the personal statement?
In my opinion no. You should mention your current work and any relation it has to doing a PhD, and that you wish to now do research and gain a PhD. Emphasize why you want to do a PhD but do not compare your current job with that. Anyone reading your reference will likely make positive inferences about you having real-world experience and that you are following your heart. Generally try and steer away from any negative comments.