"To phase out" is sort of an idiom for gradually eliminating something over a period of time. "We're in the final phase" is this case would mean we're in that phase which sees something finally disappear.
If something is currently phased out, then the "phase-out" period is over, and was successfully completed. IT'S GONE. Of course, it may be re-instituted at a later date.
If something is currently phased-out, this is really another idiom for, "it has been successfully phased out." That is, "phased-out" becomes an adjective. "That is a phased-out policy," quite different from "That policy is being phased out," which means it's still in force to some extent, but is being eliminated in stages.
Edit. GG's is quicker!
In your example, lower income taxpayers can still claim the exemptions for their dependents, and for being a person.