Hawk Diesel
Adventurer
Each one individually is one thing, though I'm not sure about the damage shield, but the three together is completely overpowered. The damage shield is particularly problematic in that it provides complete immunity from insects.
But how? Light is a cantrip. It's a ribbon ability at best, and under certain circumstances can make the character or party a target, since it would hinder stealth. The damage extra damage is neglible until higher levels, and again is a highly resisted damage type. And I don't get the point about insects. How does it make the sorcerer immune to them? And again, the minor fire shield effect is not really ideal, because sorcerers typically don't wanna be anywhere near melee range.
Is this really more powerful than the at will advantage of a wild mage sorcerer? Or a darkness sorcerer's 120ft division, which effectively makes them invisible while in darkness for any creature that relies on sight (as well as making them ideal scouts to warn the party of oncoming danger in the dark before the danger can spot them)?
Actually, that makes it worse. But your taking damage is not a limitation. And at 14th level you have Phoenix Spark anyway.
How is taking damage not a limitation? And why is it bad if the abilities have synergy? Additionally, Phoenix Spark requires additional resource expenditure. Hit dice don't automatically fully recharge on a long rest, meaning it does require determining if you wanna spend it all and have fewer hit dice the next day, or just enough to recover them all or have some left for a particularly difficult adventuring day. Without spending hit dice, this is no different than a half-orc's relentless endurance or shadow sorcerer's strength of the grave, except those examples get the ability at level 1 versus level 14 for the Phoenix Sorcerer.
I do like @Salthorae's suggestion, though maybe instead I'd limit Nourishing Flame to maybe reducing the cost of the metamagic used by 2.