Why would Spence Jr want to fight Pacquiao next? Sure, he's number 3 in the division and has the WBA belt, but he's also rapidly getting older.
It would make more sense to fight Crawford next, get the WBO belt, then fight Pacman when he's old AF. He's already almost 41 years old, won't make any difference waiting until he's 42.
Anyway, he won't get that far since Crawford would beat his ass.
In case you missed it, Spence Jr. team decided to have a clash first with Porter since they had no chance dealing with Pacquaio this year because of what I mentioned above wherein Pacquaio will dedicate to work on the Senate on the remaining months this year after his last fight with Keith Thurman.
In case he wins (and he was sure of that) against Porter, his next target is Manny Pacquaio. Then if ever he will win again, his last stop for the next year is Terrence Crawford. No way he will take Crawford first because his desire for fighting Pacquaio will not happen if ever he will lose to this one of the prime boxers today.
However, that was just his plan as Manny's camp nor Crawford's camp doesn't have a plan for now, at least as far as the reports are a concern.
I saw a betting last month somewhere wherein who will be the next Manny's, Crawford's opponent, I just forgot where I saw it.