The Phoenix is one of the most powerful cosmic beings in Marvel Comics, able to destroy stars and generate destructive power on a scale that's hard to imagine. The X-Men barely survived their initial and classic encounter with the entity in "The Dark Phoenix Saga," leading to the question of who else in Marvel Comics would be able to defeat the Phoenix.
Many powerful beings and forces exist within the Marvel Universe, some of which are beginning to emerge in the MCU. The Scarlet Witch's exploration of chaos magic could potentially lead to a confrontation between chaos magic and the Phoenix Force. It's one that's already happened in the comics, with shocking results for readers. But there are plenty of heroes who can go toe-to-toe with Jean Greye's Phoenix Force, and who have proved it in the comics already.
"The Dark Phoenix Saga" storyline spans Uncanny X-Men #129-138
25 Kang The Conqueror
Kang found the biggest loophole to taking on the Phoenix Force: time travel
In an actual fight where he is left to his own devices, Kang the Conqueror does not stand a chance against the Phoenix Force and he isn't likely to make for a suitable host either. However, Kang has one loophole that other suitors on this list don't: he has the power of time travel on his side. He has mastered all of the reality bending implications of time travel.
If Kang ever finds himself in a scenario where he must combat the Phoenix Force, he doesn't have to risk his life in an unwinnable bout against a cosmic entity. Instead, he can travel back in time to kill its host before said host acquires the Phoenix Force, or even prevent the host from being born altogether. Not even a cosmic being is immune to the complexities the timestream.
24 Echo (AKA Maya Lopez)
Echo has proven she can handle the strongest version of the Phoenix
Echo is one of the more recent hosts to the Phoenix Force and may rank as the most unexpected hosts as well. However, when she acquired the Phoenix Force, it was believed that she could even more powerful than Jean Grey, In due time, this would prove to be the case as she received the biggest upgrade in the history of Phoenix lore. There were concerns from Echo herself that she could become as dangerous to others as Scarlet Witch once was, but she manages to grasp control of the Phoenix Force.
It's clear that Echo harnesses an untapped potential as a hero, considering that she's able to handle the strongest version of the Phoenix. Anyone strong enough to control a force that powerful without being overtaken by the Dark Phoenix is powerful enough to defeat it.