Pham is the only one guaranteed a starting spot at this point. As long as he is healthy he will be the primary left fielder for the Padres all season long.
Center field battle:
In my opinion, Manuel Margot is the only true center fielder the Padres have.
Franchy Cordero and Trent Grisham are capable of playing there, but they both profile better as corner outfielders.
I don’t know enough about Trammell and Olivares to say whether or not they can stick in center, and neither are likely to break camp on the Opening Day roster.
Trammell certainly has the speed and range to cover center, the only question with him is his arm.
After watching several Winter League games of Franchy in left field, I’d say he needs to stay in a corner spot. Even his defense in left was shaky in the few games I watched.
Right field battle:
This is where things get even more complicated. You have Myers, Naylor, Cordero, and Grisham all likely battling for time in right.
Naylor is someone who has received a lot of love lately. Our own Cheri Bell pegged him as the starting right fielder to open the season, as did Dennis Lin of The Athletic (subscription required).
His left-handed power potential is probably what has people excited, but his defense was just as bad as Franmil’s.
If Preller is unable to trade Myers, you have to figure he’s going to play or at least get the majority of the starts in right.