Mages typically try and keep distance between themselves and their enemies. Although able to wield powerful offensive spells, they are particularly vulnerable to close range melee attacks. Spells such as Frost Nova and Blink are particularly useful to a mage when trying to keep their enemies at a safe distance.
Provide these conjured items to your party members when they need them. You might want to prepare some of this stuff before battle so you don't have to waste time inbetween fighting.
Conjure Food - Conjures X loaves of bread, providing the mage and their allies with something to eat.
Conjure Water - Conjures X bottles of water, providing the mage and their allies with something to drink. Players can only carry 80 Conjured Manna Biscuits at a time.
Conjure Mana Stones - Conjures a Mana Agate, Citrine, Jade, or Ruby that can be used to instantly restore a significant amount of mana. Use them on yourself in emergency situations.
You can pick whatever you want. You might find these more tailored to the mage:
Tailoring - Tailors can create Cloth armor for themselves or sell it to others.
Enchanting - Enchanters can enchant their equipment to make themselves more powerful.
Herbalism and Alchemy - They can create buff potions or mana potions.