I was leveling up the flares and the ultima spell outside of Phin. From level one to level ten I got one skill point per select/cancel and two points per use.
At level 10 it stopped giving points outside of phin so I started working on the spells outside of the jade portal.
That worked the same way; one point per select/cancel and two points per use up to level 13.
At level 13 with 98 skill points it stopped raising.
No enemies inside the jade portal or inside Pandemonium Castle raised them any more no matter how many times I used them or select/canceled.
I had already been through the portal and most of the way through the castle so there wasn't any mini boss's left guarding chests to use for leveling.
The only spells I was able to raise to 16 was cure and change.