This page explains the battle system in the Super Famicom version of Tales of Phantasia.
In battle, you are in control of Cless/Cress. Pressing the attack button will make Cless/Cress run up to whatever monster he is targeting (which you can change by pressing the appropriate button) and slice with his equipped weapon. If Cless/Cress is far enough away from the monster, press attack twice and Cless/Cress will execute a more powerful jumping slice.
If you press up+attack, Cless/Cress will stab instead of slice. As before, pressing the stab combo twice will make Cless/Cress execute a more powerful jumping stab.
However, stabbing is much slower than slicing and leaves Cless/Cress more vulnerable to attack. Some of Cless/Cress's weapons are better for stabbing and some are better for slicing, so be sure to check.
Cless/Cress's skills are described in The Menu System. Press B, or up+B at short range or long range, depending on how you have assigned his skills.
Cless/Cress always has a "home" position that he returns to after running up and hitting a monster. This home position can change during battle (explained below). Cless/Cress's party will move according to Cless/Cress's home position, staying in the formation set in the Form menu.
Cless/Cress can walk left and right. This will set a new home position. Cless/Cress's party will always follow behind him.
If Cless/Cress gets hit (even if he blocks), then Cless/Cress stops there and it becomes the new home position.
If Cless/Cress is running back toward his party after hitting something, you can make him quickly stop and turn around by pressing the directional pad in the other direction. This will be his new home position. This can be helpful, because it makes Cless/Cress turn around more quickly, allowing him to attack sooner and making him less vulnerable.
Pressing L or R in battle is different from pressing left or right on the directional pad. When you press L or R, Cless/Cress goes left or right, and Cless/Cress's party will move to his other side. You can use this to move your party to safety if there is a monster behind your party, for example.
If you stand at the far left or the far right of the battle screen and press L or R, you will run away from battle when the counter reaches zero.
If the enemy blocks a hit, it takes a moment before Cless/Cress can move away or attack again.
During battle, you can open a menu that allows you to have other party members cast magic spells, change your party members' tactics, change your party's formation, and use items. Spells and tactics are explained later.
You can't cast a spell while another spell is being cast. If a spell is in progress (including enemy spells) you can't cast a spell.
If you change a character's tactic during battle, that tactic will stay selected even after the battle is over.
However, if you change your party's formation during battle, it doesn't stay that way after the battle; it automatically goes back to whatever it was set to before the battle started.
There is a timer on the items menu in battle. If you use an item in battle, you'll have to wait a few seconds before you can use another item. There are also certain times you can't use items, such as during a spell.