The Cursed King by Abigail Owen

Airk Azdajah, the rightful King of the White Clan of dragon shifters, spent half a millennium being tortured by the false High King Pytheios. The only reason he’s alive is a curse— the man to kill Airk will be consumed in his own fire. Which is why Pytheios kept Airk alive, barely, unable to shift in his prison cage, driving the creature half of him into madness. Airk escaped, but he’ll never be truly free. What good is a king who can never let his feral dragon loose, never fly, and never lead his people? He’s better off dead.

Angelika Amon is the last unmated phoenix. The problem? She has no powers. Zip. Zilch. Angelika hates being dormant, especially now that her three sisters are blissfully mated to powerful dragon shifter kings and are very much part of the fight to take down the rotting king Pytheios, their parents’ killer. What good is a useless runt of a phoenix in a battle to save the dragon kingdom?

Desperate to find some way to help, she offers herself to Airk as a mate — just for political leverage. But a dormant phoenix is no damn use to him just like a dragon who can’t shift is no use to her. Until Pytheios sets his sights on Angelika for himself…