A CS2 Doppler phase is the version of the Doppler finish you actually received. Valve does not print the phase on the item. The pattern index picks it at the moment the item is created, and the community sorted every possible outcome into named groups. Float checkers and item databases such as the ByMykel CS2 item dataset use the same names.
For regular Doppler, the phases are Phase 1, Phase 2, Phase 3 and Phase 4, plus the gems Ruby, Sapphire and Black Pearl. For Gamma Doppler, the phases are again 1 to 4, and the single gem is Emerald.
What does each Doppler phase look like?
The numbered phases mix red, blue, purple and black in different amounts. The gems are named after their colour: Ruby is red, Sapphire is blue, Black Pearl is dark with a faint shimmer, and Emerald, on Gamma Doppler, is green.
These descriptions are enough for a rough guess, but the safe way to confirm is to run the inspect link through a float checker, which reads the pattern index and names the phase.
Which Doppler phase is worth the most?
The gems cost the most because far fewer pattern indexes land on them. Prices between the numbered phases move with demand, so check recent sales for the exact knife and phase before you buy or sell.
Phase changes nothing about the weapon in play. The value gap is purely about looks and scarcity. That gap is also why phase is a common target for mislabelled listings, so treat any gem-priced item that has not been verified by tool as unconfirmed.