Try using group_concat
:
select concat(ej.FirstName, ' ', ej.LastName) as judge,
ej.email,
ej.phone,
group_concat(ed.EventDate) as EventDate
from EventJudges ej
inner join EventJudgeXref ejx on ej.Id = ejx.EventJudgeId
inner join EventDates ed on ejx.EventDateId = ed.Id
where ejx.EventDateId in(SELECT Id FROM EventDates WHERE EventId = 1)
group by ej.Id
order by ej.FirstName asc, ej.LastName asc