In WotLK Classic Phase 4, having the Best in Slot (BiS) gear is crucial for maximizing your character's performance.
There are different BiS lists for different classes and specs, depending on their stat priorities and playstyles. For example, a Fire Mage would look for items that have high spell power, hit rating, critical strike rating, and haste rating, as these stats will increase your damage output, casting speed, and spell hit chance, while a Protection Warrior would look for items that have high stamina, armor, defense rating, and dodge rating.
Depending on your spec, you may prefer different types of gear. You can also use Wrath Classic gold to buy gear upgrades to strengthen yourself. For example, Fire Mages benefit more from critical strike rating and haste rating, while Arcane Mages benefit more from spell power and hit rating.
In WotLK Phase 4, there are several sources of bis items for Mages, such as the Icecrown Citadel raid, the Ruby Sanctum raid, the Frost Emblem vendor, and the Ashen Verdict faction. This guide helps you choose the best items for Mages and specs in Phase 4, and it can help you improve your performance and plan your gear progression.
Some of the Best Items for Mages in Phase 4 Are:
Head: 
Sanctified Bloodmage Hood (from Icecrown Citadel) or 
Cowl of Malefic Repose (from Ruby Sanctum).
Neck: Sindragosa's Cruel Claw (from Icecrown Citadel) or Penumbra Pendant (from Ruby Sanctum).
Shoulders: Sanctified Bloodmage Shoulderpads (from Icecrown Citadel) or Shoulders of Frost-Tipped Thorns (from Ruby Sanctum).
Back: Cloak of Burning Dusk (from Icecrown Citadel) or Crimson Star Cloak (from Ruby Sanctum).
Chest: Sanctified Bloodmage Robe (from Icecrown Citadel) or Robes of Azure Downfall (from Ruby Sanctum).
Wrist: Bracers of Fiery Night (from Icecrown Citadel) or Bracers of the Dark Pool (from Ruby Sanctum).
Hands: Sanctified Bloodmage Gloves (from Icecrown Citadel) or Gloves of Bitter Reprisal (from Ruby Sanctum).
Waist: Crushing Coldwraith Belt (from Icecrown Citadel) or Belt of the Fallen Brood (from Ruby Sanctum).
Legs: Sanctified Bloodmage Leggings (from Icecrown Citadel) or Leggings of Woven Death (from Frost Emblem vendor).
Feet: Plague Scientist's Boots (from Icecrown Citadel) or Halion's Spiteful Treads (from Ruby Sanctum).
Weapon: Glorenzelg, High-Blade of the Silver Hand (from Icecrown Citadel), or Zod's Repeating Longbow (from Ruby Sanctum).
Off-hand: Bloodsurge, Kel'Thuzad's Blade of Agony (from Icecrown Citadel), or Shriveled Heart (from Ruby Sanctum).
Ring 1: 
Ashen Band of Endless Destruction (from Ashen Verdict faction) or 
Ring of Rapid Ascent (from Icecrown Citadel).
Ring 2: Band of the Invoker (from Icecrown Citadel) or Signet of Twilight (from Ruby Sanctum).
Trinket 1: Dislodged Foreign Object (from Icecrown Citadel) or Charred Twilight Scale (from Ruby Sanctum).
Trinket 2: Phylactery of the Nameless Lich (from Icecrown Citadel) or Sundial of Eternal Dusk (from Frost Emblem vendor).
I hope this summary helps you find your bis items as a Fire Mage in WotLK Phase 4.
Related Link:
WotLK Phase 4 DPS Ranking Guide