The Superhero Database Classification number, or SHDB Class, is a number that represents the overall 'power' of a character. All traits of a character are used for calculating the Classification.
What it DOESN'T mean
This doesn't mean that a higher class would always beat a lower class character. But the bigger the difference in Class is, the more obvious it is who'll win in a fight.
How is this calculated
( INT^1.3 + (STR*0.5 )^2 + (SPE*0.5)^2 + DUR^1.6 + (POW + (SPS*SPL))^2 + COM^1.8 ) ^ TIER
Super Power Score and Level
Every Super Power has a score (SPS) that is used to calculate the Class. Each Super Power also has 3 levels (SPL). The level is set when connecting that Super Power to a character. The level determines the final score, of the Super Power, being used in the calculation.
Phoenix > Surfer
Durability - Invulnerability isn't really a thing, and Phoenix hosts (including ones weaker than Jean) have survived hits from Galactus. Surfer isn't going to do much.
You first voted for Silver Surfer but you changed it later on. What makes you change your mind?
m.imgur.com/a/3LKnFLL
The 2nd scan was not jean grey alone, its two phoenix's against a hungry Galactus.
The 3rd scan, poorly fed Galactus recovered in the later part of the scan and the Phoenix was threatened(scared to death) and flee. It was never a stomp because Galactus still continue siphoning the planet and a became a victor in the end. He doesn't even care or noticed Phoenix fleeing. Here is the complete battle link -> www.quora.com/Who-would-win-in-a-battle-between-Galactus-and-The-Phoenix-Jean-Grey
Again if this is the White Phoenix of the Crown, Galactus even with Silver Surfer has no chance of winning. Anyways thank you for the scan.
And Galactus explicitly says; "And I hover near to death, my strength depleted-exhausted in our struggle." This clearly shows Rachel Summers Phoenix (who is inferior to Jean Grey Phoenix, btw) is at the very least comparable to a starving Galactus, which puts her above Silver Surfer.