6,200 Ice Damage
10,800 Fire Damage
▶ 
3.3s Stun or
▶ 
3.0s Slowdown
4,300 - 4,500
+40 times each Spell
These methods are available already but scattered across the board, most of them you probably have already figured out, but it still might help players who are not aware of it. I have tested all these methods, with opponents till 4,300-4,500 trophies range (roughly about 500 medal players). I use Swordrain, Blizzard and Firestorm mostly sometimes Sonic Blast, Shield (not forged) and Toxic Cloud. None of the spells I used were boosted by any gear but they were maxed and forged more than 40 times. Blizzard damage 6200, Firestorm damage 10800, Swordrain Stun ability 3.30, with high range, Toxic Cloud with 3.0 Slowdown effect.
I'm sharing my stats screenshot to give you a picture that you don't need spell/troop enhancement items.
Stats Screenshot
Be mindful it works till 4300 trophies/500 medals, method 3 works for all level players as you might have seen in various tutorials (gathering an army and let it run its course while keeping it alive).
Pre-Requirements[]
Speed Boost of 30% or above (60% or 100% is great).- Know how to push Phoebe (it's like pushing every other beast), use tammy to practice in your defense.
- Heal or from Chloris Ring to heal and survive damage.
Method 1[]
Rush past phoebe. Do not fight it, just rush past and let your army buy you some time and use the donkey guardian to reach castle gate (taking down the castle gate is the primary objective), a variation of this method is to push phoebe beyond your troops so you can take some troops with you instead of them dealing with phoebe, and let the new incoming troops handle phoebe. If you bring Mummies along , use it to bring down the castle faster
Method 2[]
Use monks: if you have 5-7 monks push phoebe into your monk army you can face phoebe face to face with monks healing you. You can use spells to take it down (takes 10-15 seconds). It works till 4300 trophy players (with less than 400-500 medals). It's a tough method, but it can work, it's phoebe heal vs monk heal. Takes at least 10 seconds.
Method 2: Monk Army
Method 3[]
Gather a large army and push phoebe into your army of small units so your army defeats the beast very easily. Use the Shield spell for a large army, it's important. (Instead of only monks, you are using other units, also based on your choice to build an army, and push the beast into it, so it's similar to method two but more effective with the variation of the shield instead of heal from monks). Having a monk is just a bonus with the shield, but monks are not necessary as you can replace another heavy troop to take down towers or boost troops.
Method 3: Unit Swarm + Shield
Method 4[]
If you have lost your army mid-way or don't have enough units, you can defeat the beast by moving away towards your tent, and while phoebe follows you are using your spells to deal damage, always maintain one block distance so it follows while you kill it with spells, kaiser pal is helpful here as it follows you.
The picture will look like your king is followed by Kaiser and by Phoebe.
While Kaiser's sonic blast damages so do your spells. In about 10 seconds phoebe can be defeated without an army. The same strategy works with bela pal (drains phoebes health) + gargoyle (as it doesn't stop the beast but damages it) combo which a good team member of my alliance shared with me I tested it once, and it works. One important thing: your army or other troops should not stop phoebe. If it does stops phoebe, it will heal itself which is not what we want. When moving phoebe cannot heal or do damage, and we are taking advantage of that. The screenshots should give you a better idea.
Method 4: Spells + Kaiser
Other conditions[]
Make sure you have Blizzard or other ways to stop werewolves from howling because the beast becomes unstoppable till the howl effect is over.
The location where you fight should have no towers on either side of the lane (unless your army is massive), so clear an area and keep your troops in the tower-free area when you meet phoebe, as we don't want towers to kill your troops, if that happens, follow method 4 or method 1.
There may be other methods and variations, but these are the methods I use. If you have doubts post it and I will try to help.
Shortcut: The Gaspar Way[]
This section was adapted from a user's comment down below.
Apart from the ways mentioned above, there is another way to defeat Celestial Phoebe: The guardian Gaspar. His royal flush is perfect for all beasts, especially Celestial Phoebe, as it removes a percentage of the beast's full health, instead of a fixed amount. Simply activate Gaspar near Phoebe and immediately use its special ability to kill it as quickly as possible. However, as Gaspar is one of the rarest guardians in-game, finding it is a whole challenge in itself. But you can find him easily in granny shop for 125.000 magical bottles
Note: This guide was mostly adapted from the old forum thread with the same name, created by the user Surviva.