Volume of Deadlifts varies by the lifter. If the sets are maximal / near maximal at any rep range, I typically don't recommend more than 1 all out set at that weight / rep range. HOWEVER....we might accumulate a bit more volume (if needed) in the form of (1) back off sets after the main top set or (2) light deadlifts or deadlift variations on a different day of the week. When you start playing with all the various permutations of sets/reps, etc then there are a million ways to do it.
Use the book as guidance, but don't ignore your own individual feedback and response to various protocols to see what works and doesn't work. Remember the big picture stuff that's in PPST3 too that can guide you.....like that we typically raise volume on a lift when lifters get stuck for a period of time. When volume is increased then intensity MUST correspondingly come down a bit. So make sure you understand some of the bigger picture stuff and don't just follow the program examples like it's a cook book.
I have very good luck with lifters using TM programming where I have them pull 2 sets of 5 reps at 80-90% of their best 5RM on Monday and then on intensity day we alternate each week between a top set of 5 and then on alternate weeks a top set of 1,2,3. So it winds up looking something like this:
Week 1: 5RM, Week 2: 3RM: Week 3: 5RM, Week 4: 1-2RM Week 5: 5RM....etc, etc. Some lifters do back offs on ID, some don't.
The big problem with thinking in terms of "phases" like above is that it tends to make people think they MUST do some extended period of time at each phase and exhaust every last drop of progress out of each phase before moving onto the next. While there is often a natural timeline (weekly linear progress generally comes before cyclical approaches) there isn't necessarily an established pattern or timeline that every lifter MUST adhere to. If it helps, think of the phases more as "options."
Try and learn to read yourself and interpret what is going on each week and adjust accordingly. This is essentially programming in a nutshell. Observe, interpret, adjust, repeat.