You can either access them by index $row[0] through $row[10],
select FirstTable.*, SecondTable.*
from ...
or give the columns unique names (by the way, the query you posted can't possible work, I assume there's a typo in the "where" clause)
mysql_query("
select
FT.Field1 as FTField1,
FT.Field2 as FTField2,
FT.Field3 as FTField3,
FT.Field4 as FTField4,
FT.Field5 as FTField5,
ST.Field1 as STField1,
ST.Field2 as STField2,
ST.Field3 as STField3,
ST.Field4 as STField4,
ST.Field5 as STField5,
ST.Field6 as STField6
from FirstTable FT
left join SecondTable ST
on FT.field1 = ST.field1
where verizon.field1 is NULL")