In the CA PPM New User Experience (UX), for the task field of Type, there are three options, Phase,Task, and Milestone. Is there any way to hide 'Phase' value from the drop down?
There is no way to hide or delete any value for this field in the New UX.
This is similar to behavior of lookups such as Stage and Assignment Pattern in Classic UI where values of these out of the box lookups cannot be deleted (or hidden).
See the following documentation on how the values in the Type field can be used: New User Experience: Project Tasks, Phases, and Milestones
Reference KB000093171 - What are the known New User Experience (UX) defects?
Reference KB000093166 - Where can I find New User Experience (UX) knowledge documents?