It does work for skills.
Tested on level 92 Cataphract. 176 STR.
All equipment removed, 320 Physical attack.
being level 92 causes 92 physical attack.
Anyways
320 - 176 - 92 = 52.
So where is the extra 52 physical attack from?
176 x 1.3 = 228.
228 - 176 = 52.
Now. My Level 3 Bash has 173 skill damage and deals 406 damage on Tontuila which has 87 physical defense
320 + 173 = 493.
493 - 87 = 406.
Thus we know the physical attack bonus is applying.
Otherwise he’d deal 354.
52 damage may not seem like a lot (well it is at 92) but on damage weak enemies that’s 78 damage extra damage on all hits for the enemy weak to Pierce/Slash/Strike Which is already half an Arde.