Do I need the subjunctive when I say ‘conducir’ in this sentence?
A mi me pone nerviosa que la gente hable por teléfono cuando (they drive)...
Would ‘they drive’ have to be in the present subjunctive or not? I think yes but I’m not 100%.
Well, sorry but... nope, it is not subjunctive haha.
You're saying "...that people use the phone while they drive
". Let's focus on the questioned part: "when they drive".
The sentence "they drive" is a fact, it is not questioned. They do drive, the thing is what they do meanwhile, but they are driving indeed.
So it is a fact, and consequently must be indicative mood. What you're questioning is that they speak by the phone. That is subjunctive.
So your sentence is
A mí me pone nerviosa que la gente hable por teléfono cuando conduce.
I know it is hard for non-natives, but keep trying. The sentence was quite good though.
Extra:
The subjunctive doesn't fit well with subjunctive in this case. But you could hear a subjunctive, for example, in
No quiero que la gente hable cuando conduzca.
Those are 2 subjunctives in the clause. But that is implying that they are not driving now. It can be something like ap lan. They are going to drive (probably), but they are not driving yet!
So, I don't want the people to talk (by the phone) when they drive, if they do so. It's not a certainty, so that's why you'd use the subjunctive there.
However, in your original sentence, you're describing how people drive (they do drive), so that's not a subjunctive. Hope this helped.
Supplemental answer:
If you can clarify by adding "en general," then indicative fits:
A mi me pone nerviosa que la gente hable por teléfono cuando manejan, en general.
Here's an example of a sentence where the subjunctive of manejar is needed:
Cuando manejes a Houston la semana que viene, avísame cuando hayas cruzado la frontera, por favor, para que no me preocupe por tí.
In contrast, putting "en general" in this sentence wouldn't make sense (Cuando manejes en general a Houston would be nonsense).