Top / Bottom Query - ORA-00907 / Missing Right Parenthesis

I'm trying to create a Top / Bottom query from an example i already have but when i executed it, i got an error:

ORA-00907: missing right parenthesis

The coding i've got is:

SELECT customer_id, forename, surname, start_date_time, end_date_time, pos
FROM (
SELECT customer_id, forename, surname, start_date_time, end_date_time,
row_number() over (
partion by start_date_time
order by customer_id asc) pos
from customer, phone_call)
where pos = 1;

The error is on the partition line but i've closed all the open brackets,