Yeah Slyph can be pretty tough me and Sheena had a rough time with them also... Best thing to do is equip that anything that'll give your attack an earth element (that stone you get from Gnome is good if it doesn't lower things too much) and something to give you high magic defense.... Probably a good idea to be around Lvl 45 or higher too and the party we used was Lloyd, Sheena, Zelos, and Raine. I hope this helps ^-^