How could I plot a contour graph of stress increment of each phase ?

PLAXIS phase calculations are divided into multiple steps to reach equilibrium for the defined phase configuration.

Normally, PLAXIS Output will only show you the results of the last step of the phase. When intermediate steps are saved, we can also inspect the results for these intermediate steps by using the Phase/All steps toggle button next to the Phase List in Output.

From there, we can visualize any calculation step results.

Note, by default, PLAXIS will only save the last step of each phase, and subsequently, we can only see one step per phase: the last step. To store these intermediate steps, we need to increase the Max number of steps stored. This can be set in the Phase window under the Numerical control parameters.

More information at the following link:
https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/45553/inspect-intermediate-step-results-in-plaxis-output

Thank you for your kindness information.