try this
SELECT
(case
when datepart(year,getdate())-cast(yearstarted as integer) > 29 then '5'
when datepart(year,getdate())-cast(yearstarted as integer) > 13 then '4'
when datepart(year,getdate())-cast(yearstarted as integer) > 5 then '3'
when datepart(year,getdate())-cast(yearstarted as integer) > 1 then '2'
else '1'
end) as phase, *
FROM table
EDIT:
You need repeat whole case in where
AND case
when datepart(year,getdate())-cast(yearstarted as integer) > 29 then '5'
when datepart(year,getdate())-cast(yearstarted as integer) > 13 then '4'
when datepart(year,getdate())-cast(yearstarted as integer) > 5 then '3'
when datepart(year,getdate())-cast(yearstarted as integer) > 1 then '2'
else '1'
end) = <cfqueryparam value="#arguments.phaseFilter#" /></cfif>
Or create Select(your query) where phase = condition