Your XPHB improves. You add your Sorcerer level to the Temporary Hit Points gained from XPHB, and the damage of XPHB increases to 1d8.
Honed Spellfire
Raw data
{
"name": "Honed Spellfire",
"page": 25,
"level": 14,
"__prop": "subclassFeature",
"header": 2,
"source": "FRHoF",
"entries": [
"Your {@subclassFeature Spellfire Burst|Sorcerer|XPHB|Spellfire|FRHoF|3|FRHoF} improves. You add your {@class Sorcerer|XPHB} level to the {@variantrule Temporary Hit Points|XPHB} gained from {@subclassFeature Bolstering Flames|Sorcerer|XPHB|Spellfire|FRHoF|3|FRHoF}, and the damage of {@subclassFeature Radiant Fire|Sorcerer|XPHB|Spellfire|FRHoF|3|FRHoF} increases to {@dice 1d8}."
],
"className": "Sorcerer",
"classSource": "XPHB",
"subclassSource": "FRHoF",
"subclassShortName": "Spellfire"
}