I am a third year phd student. I got an offer for an industrial job which is very tempting. The salary is competitive and much higher than my phd salary. I already worked there as an intern, so I know the environment. The only problem is that I am involved in multiple projects in my phd. If I leave the group, someone has to take over those tasks, but there is no such a person in our group yet. What is your suggestion?
Taking the job would probably mean permanently leaving academia behind, and giving up the prospects of ever finishing your Ph.D. If you're okay with that (which you might well be), then I think it's fine to take the industry job.
I also recommend trying to figure out what your future job prospects are if you decide to finish your degree (and conversely, what your future job prospects might be if you take this industry job and it doesn't pan out).
The comparison to your PhD salary seems a bit strange unless your circumstances are unusual (e.g. you really need the money now). Whatever you decide, I recommend putting your own future first, and thinking less both about your present salary and about your PhD advisor.