This is how I will construct my training if I were you.

Day 1: Chest + Arms
Day 2: Back and Shoulder (Side and Rear)
Day 3: Legs + Traps + Forearm
Repeat

Reasons why I do like this:

1. Pair big muscle group with small muscle group - If you train intense enough for your first big muscle group, you shouldn't have enough energy to train intensively for the other big muscle group.
2. Compound chest exercises use triceps - Then why not train them together in the same day, then add on biceps alongside with it.
3. Your biceps are sore for the back day - Then you will learn how to use your back to pull instead of using biceps (exhaustion method).
4. Chest exercises will always effect your front and side delts - Depending on what you do, you will train more front delts than side delts and rarely the rear delts.
5. You can put more emphasis on your side and rear delt on back days - Alongside point 1, you can properly train your side and rear delt which usually will be neglected. 3 isos exercises for rear delt should be good to prevent shoulder impingement.
6. Don't forget your traps and forearm - Train them forearm, traps and forearm like you would train your other muscle groups. Did I said forearm twice? Yeah.
7. Where's the abs? - Do when you want to do it. On your rest day perhaps?

Just my 2cent opinion from my experience of doing PHAT.

p/s: If you have flexibility for the rest day, take a rest day after your leg day. You will start fresh for your next cycle.