The drive time to within 10 miles of PHX is <60 min, then it is another 30 min to get to the car rental center, and another 30 min to get by bus to your terminal -- yes, it is that slow most of the time!!!! Very inconvenient rental car arrangement at PHX (for which they charge a huge surcharge). T4 security can take 1 hour at that time of day (much less at T2 and T3). Most airlines have 45 min cutoff at PHX (longer than at most airports), so you also need to take that into consideration. So 6 am departure is about the latest without cutting it too close.